Markait (previously called Sanctum or Sanctumverse) was my first attempt at making a Sci-Fi setting. When I made it, I didn't know what I wanted it to be or what I people would find when they played it. Its evolved into an interplanar refuge galaxy to save peoples and entities from certain doom had they stayed in their own galaxy. The Great Builder, Shinome, has a mission for Markait. Though this mission is not totally known it seems to involve the preservation of all manner of flora, fauna, minerals, and oddities of not just the next galaxy over, but nearly from every corner of the multiverse. He doesn't seem to care much what they do when inside the sanctum, for some reason they hold less interest to him as soon as they're in the Markait itself.
I suppose the primary purpose of Markait is to practice making other settings. I also suppose it is also practice in using World Anvil too now that I think about it. Much of this will show in the fact that a have a lot of names and locations but very little substance to go with them, much of this is fluff to make sure there is plenty of galaxy to visit for the players as I'm usually a Free-Form GM with very little in the way of planning, preferring a pick your own adventure strategy with players. That said, I find myself putting more and more time into this "practice setting" than I have the ones I intended to work on. Let's see how far I can take this, shall we?