I'm looking for an iPhone app that will allow me to set up a chess problem and work out its solution. I've seen apps that present me with a battery of chess problems but don't allow me to set up my own. I've also seen apps that allow me to play chess starting from the opening position. But I haven't seen one that will allow me to configure the board as I choose. Admittedly I haven't tried every existing iPhone app but none of the ones I've looked at allow this.
The only chess app on my iPhone is Stockfish, and it has a menu option Game -> Edit position where you can set up your own board. You'd also have to change the Level/Game mode to 'Two player'.
It's a free app.
Mastersoft makes a Chess app, with similar modes to Glorfindel’s answer.
I do not remember if it was free.