It's free software (https://github.com/lichess-org), and you only need web browser to play [1]. Even Magnus Carlsen and many other top Grandmasters play there.
As for cheating, all games are checked for computer play, so even if you can occasionally lose a game or two from a cheater, he will be caught, and you will get back your rating points (if you care).
[1] Dunno what they are using for latency adjustments on lichess, but it seems to work fine. No external software necessary, unlike chess servers of yore: https://www.freechess.org/Help/HelpFiles/timeseal.html
I feel that chess Tempo has really given me tools to recognize recurring tactical motifs in actual play.
I'd love at app that really plays at my skill level, but my experience with older software was that the computer "dumbed itself down" simply by playing completely silly moves at times. (Of course, I played silly moves as well, so maybe it was accurate... But it didn't feel that way.)
I've started reading chess openings and tactics as a way to send me to sleep, on one of those chess sites that sets up a play for you. I don't think I'll ever play chess again - time is limited and I don't think anyone would suffer playing with me given what I've forgotten - but I'm enjoying learning strategies again. It's great stuff for the brain.
I've put the Chess Tactics site on my weekend-lazy-reading list. Who knows, maybe I find my way back to playing games again.