This app was mentioned in 3 comments, with an average of 1.33 upvotes
I like Tactics Trainer for tactics. Although you have to pay a bit for offline tactics. https://play.google.com/store/apps/details?id=com.thecvsi.tactictrainer&hl=en
I think Shredder chess (also paid) has the best AI to play against - most human like play rather than kicking your ass for a while, then giving you a free knight before kicking your ass some more.
The best chess app overall is probably Droidfish. It free and has the stockfish engine in it. It's good for analysis and reviewing game pgn's. I'm pretty sure it doesn't have any training tools though unless you have some problems in pgn form and play them out against the engine.
Are you talking about this one: https://play.google.com/store/apps/details?id=com.thecvsi.tactictrainer&hl=en
"Tactic trainer" is a pretty general name, so a link would be helpful
TacticsTrainer is the best android app I've found for free.
It's unforgiving but satisfying.