Keep in mind that chess engines don't work by themselves. They're programs that need to be installed into a a graphical user interface (GUI). ChessBase offers the most popular one for sale. Arena is a free GUI. You can even download Tarrasch Chess, which comes with Stockfish already installed.
The chess world is mostly Windows based, but Mac users can have their fun, too. Most engines have a number after their name. This is the version number, with the higher number being the most current version.
Don't be discouraged. These programs beat nearly everyone most of the time. Nevertheless, having a program that's stronger than you are has its advantages. These programs share their evaluations with you so you can see where they think you made a mistake. They also suggest improvements in your play, which can be a very useful tool. By studying where you went wrong and considering a program's suggestions, you may learn some valuable lessons that can elevate your future play.
Here's a summary of some of the most popular chess engines out there:- Fritz is not the world's strongest chess engine, but it is plenty strong enough. Produced by ChessBase, the program should be well maintained for the foreseeable future. It is relatively easy to learn and fairly intuitive to use.
- Houdini is a state-of-the-art chess engine for Windows. Many of the world's best players have adopted it as their engine of choice. Its name was chosen for its ability to escape seemingly impossible positions.
- Crafty is a Windows-based chess program written by Robert Hyatt — a retired University of Alabama at Birmingham computer science professor — with continual development and assistance from Michael Byrne, Tracy Riegle, and Peter Skinner. Tord Romstad, the author of Stockfish, has described Crafty as "arguably the most important and influential chess program ever." Crafty has been available free for years on the ICC.
- Stockfish has been an open source engine available on various desktop and mobile platforms. It was developed by Tord Romstad, Marco Costalba, Joona Kiiski, and Gary Linscott, with many contributions from a community of open-source developers. Stockfish is consistently ranked first or near the top of most chess engine rating lists and has been the strongest open source chess engine in the world.
- Komodo is a Windows-based engine developed by Don Dailey and Mark Lefler, and supported by chess author, evaluation expert and grandmaster Larry Kaufman. Komodo is a commercial chess engine, but older versions (7 and older) are free for non-commercial use.
- Stockfish (See above.)
- Shredder is a chess program by Stefan Meyer-Kahlen. It is one of the most powerful engines available to Mac users.
- Hiarcs is another powerful engine available on multiple platforms, including the Mac. It has been around for a number of years and can be expected to continue to well supported for a number of years to come.