Exercises on lichess are one of my favorite ways to kill time. Haven't played a real game in years but I love the low pressure of running through little scenarios, even if I can't always grasp why the computer thinks a particular line is optimal lol
What were you looking to do with it mostly? Lichess is good for learning (puzzles, ranked matches, etc), and for offline analysis and local play, I recommend DroidFish. It's ui is a bit archaic, but in a good way. It's got a pretty full feature set, and the stockfish engine is excellent.