QtHello is an Othello game and toolkit.
Its design makes it easy to extend both the computer player and human player interfaces. It currently has 6 different computer players ranging from completely random to tree search with Alpha-Beta pruning.
It's mainly meant as a toolkit for Othello developers wanting to concentrate on the AI routine and not the GUI. Although I think normal Othello entusiasts might find this game enjoyable especially when the computer players get smarter.