Houdini 1.5 is the best free engine you can get. I also enjoy Lucas Chess. It has 20 engines to choose from- Stockfish, Rybka, Critter. Plus a whole host of training ideas and a pgn reader!
chess program

There are many options, but I'd suggest either Arena 3.0 or Scid vs. PC. Winboard is a 3rd possibility. (Houdini is an engine that can be installed in graphical user interfaces such as Arena, Scid, or Winboard.)
Links are in this other thread:
http://www.chess.com/forum/view/chess-equipment/best-5-free-chess-software
hello
i am looking for chess program that able