I don't see a good open source way to do journaling. Ephemeral notetaking is basically solved by Google Keep, but I think it would be really cool to have an app that loads instantly, and just gives you a box to add stuff to the day's markdown file(To sync with SyncThing, no cloud stuff needed), plus a calendar, hashtag indexing, and search.
I also think it would be cool to manage bookmarks the same way, share it to the bookmarker app, and it makes you a file with the content of the page when you bookmarked it, and the link, and a markdown metadata/notes file.
I really like the almost totally unstructured, opinionated, and search based Google Keep approach, I didn't really use the graph view or plugins besides daily note when I was using Obsidian.
Another idea I had was a tiny device with Bluetooth and NFC that acts like a digital logbook, you can put it in a work area, and if you are in range and paired with it, you can write notes into it, that sync with your local folders, and that other users can access too. The intent would just be paper-like use cases, so 1MB of flash could be enough, but you could do more with extra storage.
If you made them cheap enough, and the software was nice and easy, perhaps it could replace printing emails and handing them to people!
I've also been interested in building a Bluetooth antitheft motion sensor, so that you can leave a bag in the other room at a party, and nobody can open or move it without you getting an alert on your phone, so you can go investigate.
