What about running a Windows emulator can you do that with a MAC?
http://www.chess.com/download/view/free-chess-engines-for-mac
http://www.chess.com/forum/view/chess-equipment/chess-engines-for-mac
www.cln.org/searching_faqs.html Some people get pissed when I throw this link in I hope you don't just type "free MAC chess engines" into a search engine and you'll get lots more hits, info, etc.
I was actually looking at those before but none of them work for me
I'm a PC user so can't help out much here, maybe you should consider joining a MAC forum as I strongly suspect the vast (well big anyway) majority of members here are using PCs.
Stockfish, Critter and Komodo3 all have free Mac versions and are all very very strong. I place the latest Macintosh versions of these at www.box.com/chessx . I build stockfish from the latest source code so it is more recent than the official download site. I also build the latest version of ChessX for the Mac ( a great free open source pgn browser ) which can run the chess engines listed. ChessX has an extremely nice user interface however the official ChessX site downloads are about two years out of date compared to the source code which has has numerous improvements so I provide these builds as a convenience for Macintosh users.
You can download:
chessxForMac.dmg and stockfishForMac.zip
install chessx and go into preferences on the engine tab and locate the unzipped stockfish file, load a pgn file, or enter moves and you can view the engine output in the analysis view. I suggest loading either the new mahogony boardstyle under preferences.
The best commercial Chess GUI by far for the Macintosh is "HIARCS Chess Explorer" http://www.hiarcs.com/chess-explorer.htm for the Macintosh which seems to be based on the ChessX code base with far more features, and of course will run all three engines listed above.
Of the three chess engines, Stockfish might be the best all around engine. It is about the same strength as Rybka, maybe even slightly stronger. Critter is a great engine for tactical positions. Critter will generally find tactics much quicker than stockfish but doesn't have anywhere near the understanding of closed positions that Stockfish does. Currently according to http://www.computerchess.org.uk/ccrl/4040/ Stockfish is rated as the second strongest engine overall to Houdini, but Houdini is commercial and only runs on Windows, while Stockfish is free, open source, only slightly weaker, and runs on the Macintosh as well.
any???