Which was unknown to me (which also means nobody knows it - let alone uses it - on a large scale). Unity as a widget set is rather well known. Unity as game engine is not. Change the name...
You certainly have this backwards. Unity (the game engine) is effectively tied with the Unreal Engine for "most popular game engine in the world." It's a
billion-plus dollar endless cash cow for its developer (Unity Technologies). 99.99999% of anyone who is remotely tech savvy would think of it first if you simply mentioned "Unity". Unity the Ubuntu skin (calling it a "widget set" is something of a stretch) is on the other hand generally only known by people who both use Linux in general (which is not that many in the grand scheme of things to begin with)
and on top of that specifically use Ubuntu as their distribution. Its developer, Canonical, is a sub-100-Million dollar company that again, generally only Ubuntu users have ever heard of.