GoGlance is a Go training app for kyu players that want to reach dan level. For each problem, two moves are displayed with the ability to look at each move in isolation. A variation for each move can be explored and compared. Choose the move that you think is best and the answer is displayed. After mastering the "two choice" option for the problems, you can change the setting to instead guess the correct move.
Use an SGF editor to mark correct moves in a game with circles or triangles, and paste the SGF to import your own problems.
Go problems can be studied on the Apple Watch so that you can study Go wherever you go!