It’s more than that, it’s a whole engine and launcher combo for (mostly) voxel games, most of which again are Minecraft like, but some are very different. It’s made some huge leaps recently, graphics wise and functionality wise. The promise of the engine is also being fulfilled with more original game projects being developed for it.
Sort of, yes. In it’s earliest stages it was just an attempt at a FOSS.Minecraft like game, but it evolved into the engine/platform it is over the past few years. Minetest uses LUA as a.scripting language, which I believe Roblox also uses.