one project that comes to mind is @raphkoster's criminally underappreciated Metaplace
https://en.wikipedia.org/wiki/Metaplace
it was a little like being able to build your own 2d graphical MOO/MUD, but strongly bent towards the web. it had a scripting language and a flash-based graphical editor. i wish there was more info out there about it.
Metaplace Postmortem (2008): "Snow Crash is a Lie"
jussst after i wished there had been some kind of postmortem done on raph koster's Metaplace, i found out that he himself presented one at GDC 2008!
https://www.gdcvault.com/play/34/Metaplace-Postmortem-Reinventing
if you're not familiar with Metaplace, I don't blame you. It was an attempt at making a web-based graphical MUD/MUSH/MOO/MMO virtual world development system that could be played online in any browser. it disappeared almost as quickly as it was developed.
what i find most fascinating about it was that it had a Lua-based scripting system called Metascript. it featured some really hot runtime behaviours like being able to load/unload scripts on any object. (which means you never needed to recompile to test your world)
