this is the simple GUI with enginer Rybka 2.2n2, very simple so you could learn it well in 5 minutes, but it is good enough as the tool for studying chess books.
when I study the chess books, I need to setup position, and then think and move, I need to understand each move by white and black.
yes, Acquarium, Fritz, Winboard, arena and lots of other ones could do the same, but they are too big or too trouble, if you want to:
"start playing against the engine of your choice with either color from any position at any time."
please see more at
http://www.triplehappy.com/
of course,it still has some rooms to be improved.