If we’re talking stuff on F-Droid, the big one there for me is UnCiv. It’s an excellent fully-free reimplementation of Civ V… with all the nightmarish one-more-turn-oh-God-is-it-dawn addictive problems that implies. Only real flaw is that by adapting Civ V, it also adapts Civ V’s big flaw: traffic jams. Unciv units neither stack nor combine so waging war in an obstacle-rich landscape is hellishly tedious. Also the higher difficulties feel just abusively random and unfair because the hard-level AIs get free resources, but that’s normal for a Civ game.