I love Endless Sky, it’s honestly one of my favorite games! I have a pack of cool SciFi art that I found on Nexus and I’ve been slowly replacing the stock photos for my personal game. I’m also a sucker for TeeWorlds, it is delightfully infuriating and hillarious to play. I know that’s baby’s first FOSS games but I’m new to open source games. That’s why I want to hear your recommendations and see what are some other good ones out there.
My personal favourite is Dungeon Crawl Stone Soup, although it’s quite tricky to get into and still brutally difficult, even if you are in it.
It’s similar in concept to Shattered Pixel Dungeon, which others have mentioned here. Maybe try that one first. 🙃