Bumping this thread to add this app as a contribution.
Also from the Apple App Store.
I use it to play with my eldest who lives in South Carolina (I’m in IL).
Bumping this thread because it’s later than my thread. I’ve just finished my first game of Go on this site. I played on a 9x9 board, and lost by 84 points. I’m not getting it. I’d seal off a territory, and the white stones don’t disappear. I’m guessing that you have to be directly adjacent to stones or line of stones, surrounding it/them, like outflanking someone in Othello. But then it looks like I could outflank someone by putting a stone in the middle of four stones with one of mine on the other side, and it won’t let me move there.
I think that the only way I’ll learn this game would be to have a live tutor who could tell me why I can’t move somewhere, and could offer advice as to where to move and why. Even if I could find one, it’s pretty much assured that our schedules would not coincide. 
The actual rules, like what moves are legal and what’s the score, are super simple (though there exist slight variations), but you have to figure out by experience how to make shapes that are “alive” and capture actual territory. It may be obvious to experts, but usually one can just play on until it becomes clear.
You mean this?
I suppose. As I said, I think I need to play with a mentor.