Have a look at the game "Tera" made with Unreal engine. It is available on Steam for free. You find there very complex avatars, with scripted flexi mesh clothes, landscapes with a quality and a fantasy rarely seen in SL, and all the structure of SL components: local inventory, tough permission system, trade, chat, banking, NPC's of the Animesh kind, Huge cities , villages; road, fly and flying vehicles, non buggy teleportation, no sim borders. Of course it is a game as a whole. Which means all ressources are game-oriented which also explains the following. What is missing, because it is locked, is access to the building editor, elaborated chatting system similar to SL, but most players join discord groups, or individual discord room, what many SL resident do too.
Really, if you visit the game, keeping SL ressources and structures in mind, Unreal offers an amazing potential. I often thought Tera has exploited a lot of Second Life ideas. These two worlds are so not hermetically closed to each others: some Tera avatars and NPC's are found on our Market place ...