NEOS (AKA NeosVR) is a massively-multiplayer online virtual world platform created in a heavily-modified version of Unity. Compared to other similar platforms, NEOS is unique for its in-game content creation system, as well as its in-game scripting system that is similar to Garry's Mod Wiremod.
Unfortunately, it tied development to an in-game cryptocurrency, which resulted in it being banned from the Steam Store. The development of the game is now stalled due to a lawsuit trying to get the head developer removed and his cryptocurrency with him, due to accusations of fraud.
Many people are also turned off on the game due to the high concentration of furries.