The owner of a "place" (game saved from the editor to the Roblox cloud) can set the permissions for who can participate in the live, collaborative, editing environment (invite basis), and who can play it (public, friends, or editors).
The only problem with the collaborative editing (which is very very cool) is that it's really easy to click and delete/move/duplicate huge chunks of the game without realizing it. But, if you save often, the built in version control is really nice.
It's pretty neat though, except for the marketplace is absolutely filled with assets that contain malware. A script can be linked with any object in the game, used to give the object life. But, that script has nearly global control.
I think the scripting and standard libraries would really benefit from a huge overhaul, but it's pretty neat. There's quite a bit of friction getting started though. Much of it isn't intuitive, with magic undocumented names required, and you'll usually find well meaning, but very beginner, game developers providing colorful information in the forums.
