What it does today: - Full packet layer for the classic UO client (login, movement, items, mobiles) - Lua scripting for item behaviors (double-click a potion, open a door — all defined in Lua, no C# recompile) - Spatial world partitioned into sectors with delta sync (only sends packets for new sectors when crossing boundaries) - Snapshot-based persistence with MessagePack - Source generators for automatic DI wiring, packet handler registration, and Lua module exposure - NativeAOT support — the server compiles to a single native binary - Embedded HTTP admin API + React management UI - Auto-generated doors from map statics (same algorithm as ModernUO/RunUO)
Tech stack: .NET 10, NativeAOT, NLua, MessagePack, DryIoc, Kestrel
What's missing: Combat, skills, weather integration, NPC AI. This is still early — the focus so far has been on getting the architecture right so adding those systems doesn't require rewiring everything.
Why not just use ModernUO/RunUO? Those are mature and battle-tested. I started this because I wanted to rethink the architecture from scratch: strict network/domain separation, event-driven game loop, no inheritance-heavy item hierarchies, and Lua for rapid iteration on game logic without recompiling.
It's very different from modern games, where each player looks like the fantasy version of a Marvel super hero.
Modern MMOs are theme parks where everyone gets the same ride (with pay per win). UO was a living world where your role emerged from what you chose to do, not from a quest marker telling you where to go next.
Sort of. They disabled big parts of the "real economy" in beta. Turned out that players didn't like it that NPC shopkeepers kept standard working hours and didn't want to buy their 5000 skullcaps from their skill grinding.
Likewise they even more quickly got rid of the real ecology feature, both because it was computationally intensive but also because players would strip mine the ecology.
I've experienced it first hand, but I can't grasp why it worked well like it did.
WoW in 2004 truly scorched the field; after that MMO became synonymous with WoW clone. The same action bar, the same pov, the same control, the same short "kill 10 kobolds" quests with an exclamation mark, the same progression...
I was big into MMOs a long time ago. But I never imagined that 22 years after WoW the field still wouldn't have produced another gem in the level of UO or SWG.
UO was the last MMO that made the mistake of trying to be a world for everyone to live in.
The whole point of the game was to live in this fantasy world, not beat it. There were no quests. No antagonist. Just good and evil and everyone in between. For once I wish a studio would take this to heart and build something like that again. Minecraft exploded due to this sandbox nature. However, you still got to give players a shovel and a bucket.
I loved Everquest and World of Warcraft but those didn't feel "raw" enough for me.
The Realm is my dark horse submission for best MMO. (Yea, yea, yeah Meridian 59 and Underlight too)
I think this changed during the Mondrian era but in my favorite era, SA/Renaissance, those were the baddies that made you run.
Lich King as well.
In an odd sort of way I suspect UO would have been better off had it come out a year or two earlier. It'd not have been remotely as popular, but wouldn't have attracted such a large crowd. And because they drew from a much larger crowd than the intended audience there were a lot of people who got disgruntled. But it makes sense because the game was literally not designed with their desires in mind.
This is honestly the best way I have ever heard this described! It really is that 'end of the road' feeling that I get, once I have experienced a large chunk of the game loop, that has me disconnect from games and feel hollow.
This is probably why I keep going back to huge modpacks for Minecraft with a friend. It is so open and expansive, with so much to do, that you never really feel like it's the end... You just feel like you have had your fill, until next time.
I personally only got to watch my older brother play UO, and then he brought me into the launch of WoW which was a pivotal experience. But the end game always felt like it falls flat.
I played on the JP/KR asian servers in a PK/APK/PVP guild so maybe it was just my bubble but it was pretty common to see players with 7 skills maxed out. If I remember correctly
- sparring
- swordsman or fencing
- magic
- magic resistance
I don't remember the rest. It's not quick or easy like modern games, but we would regularly power level each other's alts and it took maybe 2 weeks to max out all 7 skills? We had a bear trapped in the guild house so we could power level wrestling and other combat skills.
It sounds like a fan-driven reboot of this game has a fairly decent following, in a very similar way to what UO experiences? It feels like there is still player desire to have mundane sorts of immersive RPG experiences in this way.
Haven't put any time in MMORPGs for 15 years, but aren't there still "exclusive" guilds that do things regular players can only aspire to?
It was a sad day when UO introduced Trammel.
>It's very different from modern games, where each player looks like the fantasy version of a Marvel super hero
But isn't this true for most games?
>UO was the only game that I've ever played where you had "commoner" players. A lot of players failed to scale up, or to obtain top notch equipment.
I guess the main example I'm thinking of is Path of Exile. There is such a massive difference between your average player and the top tier. Or even not the top tier but enthusiasts.
I mean almost by definition most people wont have top notch equipment?
This endeavour sounds a whole lot like a server emulator for Infantry Online that was started by an incredibly talented developed 16 years ago ("aaerox"). I found the original svn commit on Sourceforge [1]. It's since moved to GitHub but has been active for 16 years and it has much of the same functionality you've already built, but done by more than a dozen developers over a decade-and-a-half.
Kudos to you. You've gotta explain how you've managed to do so much all by yourself.
[0] https://github.com/moongate-community/moongatev2/graphs/cont... [1] https://sourceforge.net/p/infserver/code/1/
the big picture question is, if you can mess around with the bot to do anything, why spend it on this game? why not make your own original game instead?
In hindsight I am very glad Origin was not overly litigious and didn't send the FBI to my house for "hacking" their game.
When I was in high school, I played a lot of UO. It was actually the last computer/video game I ever played regularly, because I convinced myself as a teenager that I was addicted to it and needed to drop it "cold turkey" to focus on academics and extracurriculars.
(A sign of the times for the late-1990s nostalgics: I sold my UO account on eBay for a few thousand dollars and an MTG Mox Pearl. I owned a bunch of virtual real estate, e.g. a UO tower on an island only accessible via moongate. The high bidder "threw in" a Mox Pearl as a kind of informal escrow, to make sure I completed the account transfer after getting paid.)
Before I dropped UO from my life, I discovered UOX. I was learning C++ and UOX was a great way for me to practice my emerging C++ skills.
My clearest memory of feeling the power of programming was when I created a mod for my UOX server that allowed me to drop an unlimited number of interconnected and color-coded moongates all over my server, creating something akin to the feeling of the game "Portal," but long before Valve released "Portal."
It was after having a blast with UOX that I decided to dig into programming much more. Somehow, the UOX server mod made programming feel "real" for me in the way my prior forays into coding simply didn't.
That led to me learning Python -- as a way of toying around with the Slackware Linux server I had in my basement. I left C++ behind, but it was an important stepping stone for me. Now, decades later, learning Python was probably the single most important decision of my life in childhood. (See e.g. https://amontalenti.com/about)
UOX is such a cool project. UO was a really ahead-of-its time internet game, as well. Great memories. Thank you.
Projects like UOX3 are a big part of the history of the Ultima Online emulator scene, so it’s great to hear from someone who helped maintain it.
Curious about the sector-based delta sync — how do you avoid packet bursts when a player enters a busy area with lots of items and mobiles?
Also interesting to see NativeAOT used here. Was that mainly for deployment simplicity or performance?
On sector sync bursts — this is something I'm actively tuning. Right now when a player enters a new sector, we sync all ground items and mobiles in the surrounding sectors (configurable radius). For busy areas that can mean a lot of packets at once. The current approach is:
- Sector enter sync only sends the delta sectors the player wasn't already seeing, so a simple move into an adjacent sector doesn't resync everything
- Sectors close to the player (within 1 of center) are always resynced because the UO client silently drops items beyond its visual range (~18 tiles), so you need to re-send them when the player comes back
- The outgoing packet queue handles the actual send, so the game loop isn't blocked waiting for network I/O
That said, there's definitely room for prioritization (mobiles first, then nearby items, then distant items) and spreading the sync across multiple ticks instead of one burst. It's on the roadmap.
On NativeAOT — honestly, both. The single-binary deployment is great for Docker (small image, instant startup), but the real win is predictable performance. No JIT warmup, no tiered compilation surprises
mid-session. For a game server where you care about consistent tick timing, eliminating that variable is worth it. The tradeoff is you lose some runtime flexibility, but source generators fill most of that gap
(packet registration, serialization, etc.).doesn't look like there is much going on to protect packet bursts there aside from smart-ish proximity sector loading. the work is done at boundry.
dove into it because i have been recently working on frustrum spawning to reduce net burst in a similar project, was kind of curious if something similar was used as a method to pre-warm the upcoming sector but I didn't catch anything.
fun and easy to read. thanks op and parent for getting me to look through it.
One maybe obvious way would be that asking for rumors will actually creates the scenario that the NPC describes.
Do you have a YouTube that shows off the progress of what's complete?
I'll probably add a short demo gif or video to the README at some point, but for now the best way to see it is to clone it and run it
My brother and I bought IX when it was released but it was a buggy nightmare so we gave up and never experienced Ultima proper. However, my brother and his friend got into UO and played a ton. His friend was a greifer at the time going by the name SirDarkSpell and supposedly made a bit of a name for himself. This was around 2000 or so? I bet the two of them would love to hear about this project as both of them have fond memories of UO.
Anyway. Might just throw my weekend into the Stygian Abyss...
https://github.com/moonsharp-devs/moonsharp/releases
I'm not the creator of MoonSharp, just a maintainer on Github (who has honestly done very little). However, I consult for Berserk Games, and we have use MoonSharp as the scripting runtime for Tabletop Simulator.
Obligatory nitpicky aside, a time-honored tradition of HN:
I've long been irritated by the use of the term "server emulator" in gaming contexts. Technically these projects are just reimplementations of a proprietary networking protocol. Nobody calls Samba a "server emulator" because it reimplements the Windows file sharing protocol, because Samba isn't "emulating" anything from the perspective of the traditional definition of "emulator" in computer science.
But for some reason, I guess because "emulator" has colloquially been redefined by non-CS nerd gamer normies as a term for software that lets you play proprietary games on platforms they were not designed for, we have ended up in this new status quo where the term's definition has expanded in this game of telephone way that annoys mainly me and not many other people.
And what's kinda funny is I say that it is a "new" status quo, but it's not even that new. I recall, what, like 20 years ago now I was in an edit war on Wikipedia fighting with people over the "server emulator" article, insisting that the term was technically inaccurate and should not be used. Unsurprisingly in retrospect, I lost that edit war.
Nowadays the whole thing feels like my first "old man yells at cloud" moment, of which I'm sure I'll experience more as I age. I certainly do find new slang introduced by gen Z like "he got the riz!" to be quite cringey, so it looks like I'm well on my way to getting crotchety and terrible about the natural evolution of language! ;)
That said, I'll take the nitpick as a compliment :) means you actually read the project description. Thanks for the kind words! > other example Mangos is "Wow emualtor"
I think the distinction is a lot greyer than the black/white you propose.
The very first popular online games used servers mostly to redistribute (and maybe time sync) packets from clients. There is no standard way to to do that. Player-created servers did their best to emulate the official servers logic but it was indeed impossible to replicate it perfectly.
e.g. when breaking up large maps into sectors, the official server might broadcast your location and projectiles X units away and emulators would broadcast it X + 500 units away, which could have an impact on gameplay.
Emulator feels fitting when there is no official server spec to reimplement.
edit: emulator also feels appropriate where servers are responsible for NPC activity or quest-like mechanics. This goes beyond implementing a network protocol. The gameplay is massively impacted.
You're not wrong that "server emulator" is a generically correct use of the term emulation, in the same sense that it is a correct use of the word for someone to say they emulate a fashion sense of a celebrity they like in their own wardrobe.
But in computer science, strictly speaking, the original definition of emulator was more strict. It was about things like emulating processor architecture A so as to execute programs written for it on processor architecture B.
And part of why expanding the definition to include "server emulators" annoys me is why has this definition expansion occurred only in gaming contexts? If a free UO server is a "server emulator" then why is Samba not also a server emulator? The lack of consistency is irritating to me, and it only happened because gamers like the term emulator, not due to any kind of rigorous computer sciencey reason.
This is interesting to me, if only because it's such a natural bit of slang. Given that it's a shortened form of "charisma", this one just Makes Sense to me! I figure it'd be incredibly cringe for me to use at my age, but it's a good term IMO.
There's been research by linguists (John McWhorter comes to mind) analyzing this phenomenon and it basically just comes down to the fact that as we age, we get more set in our ways, so the linguistic innovations that younger people do just have a tendency to annoy us, even when they logically follow or are objectively useful.
I try not to let it bother me, because it's irrational to feel that way, but it just does lol
All the recent LLM advances would make for very interesting and very fun NPC interactions in a MMORPG today too. Even small player community servers could be viable long term because of the ability to seed complex interactions with NPCs into on-going story lines.
Throwback!
Pretty sure I still have the source to SphereServer sitting somewhere on my NAS. It was my first exposure -- in early high school -- to coding in a group and operating a Linux server.
I've been building a MORPG version of a kind of Ultima 3.5 on the side in spurts for the last 5 years using Go, postgres, and React on the frontend. Top view tile graphics, old school keyboard control/commands. It's pretty janky still, but I hope to do a Show HN at some point.
I think I need to take some inspiration from you and partition the world into sectors, I have a n^2 scaling problem right now as there are more PC and NPC in the world.
They've reworked a lot of systems and it's basically 100x better than original UO.
There are several systems in place, which original devs wouldn't even dream of and saying that, official Ultima Online is still running. :D
It's PvP server, but with balanced PvP which really works for everyone. Not like original devs, they just dropped PvP because cookie-cutter players cried.
Personally though, I feel they've overengineered it a bit. So many custom systems layered on top that it starts to feel more like WoW with UO graphics than actual UO. The original charm was in the simplicity you, a sword, and a world that didn't care about your feelings. But that's just my taste, and clearly thousands of players disagree with me, so what do I know. And yes, the fact that official UO is still running in 2026 is both beautiful and insane
Does it have something to do with the fact that we already have plenty well established Ultima online server emulators in the training set of your llm of choice despite you claiming it is from scratch?
But I would love to play some old school UO again with people
I spent many many hours in UO when I was young.
It was so great playing in some shards with hundreds of real persons.
"Who owns the UO IP now and how litigious are they?"
Ultima Online launched in September 1997. The first "offline emulator" launched in October. Emulators became playable by mid 1998. https://www.uox3.org/history/timeline.txt
Are there UO clients besides the official one?