Droidfish on Android, Smallfish on Apple. Chessbase is $9 but well worth it. There's a myriad of other apps out there, including free tactics puzzles. You just have to browse through and try different ones til you find one you like.
Max Chess from Google Play. It has unlimited puzzles
Chess Tactics on IOS
It has daily easy, medium, and hard puzzles.
Shredder for Android phone