PC Based Chess Software
If you play Chess on your PC then you can place a review of the program you use and the pros and cons about it within this thread.
GNU Chess is a free program that provides truly challenging chess matches for you to play.
Pro:
Realistic play
Adaptive opposition
Truly difficult
Cons:
Even on the easiest level, very hard to beat. In fact, I have never beat the computer.
I played GNU chess and I agree with konquererz. It's pro. I managed to get some draws, nothing more (not that I'm a good player). And only on the easiest level. What I don't like is that at higher levels it takes too much time to respond.
Chessmaster 7000
This is a great program. When I first came to Argentina and did not have access to the net as yet I was playing this a lot. What is great about it is that you have people with varying personalities to play not just the professional computer imitation, this helps build up your own style and weaknesses - highly recommend although I am sure there is a higher version out now. In addition to this it has a library of plays, problems to solve, a tutor, voice, 3D view, and rank system.