Sigma Chess is one of the best free Mac chess games available to download. It has a true perspective 3D color chess board.

Instruct Sigma Chess to annotate games with its analysis, or add your own free text annotations including diagrams and move suffixes.

Adjust the playing strength to your own level simply by setting the ELO rating for Sigma Chess, and choose among the many playing modes, levels and styles.

You can choose among the various piece sets, board types, types of move notation, colour schemes, the true perspective 3D board etc.

Sigma Chess is a master strength Macintosh chess program for both OS X and Classic Mac OS.

Here are some key features of "Sigma Chess":

· UCI Engine Support
· Sigma Chess 6.1 supports the UCI (Universal Chess Interface) protocol, so you can run other Mac OS X engines in the Sigma Chess GUI. The World Championship strength HIARCS 12 engine is bundled with Sigma Chess. Click here for a list of UCI chess engines for Mac OS X (UCI is not supported on Mac OS 9).
· Hosting of Engine Matches
· Sigma Chess 6.1 can now host matches between UCI chess engines.
· MultiPV
· The MultiPV (k-var) option is now available for UCI engines supporting this feature (such as the registered HIARCS 12 engine).
· Native OS X Compatility
· Sigma Chess 6.1 is a so-called "Carbon" application that runs natively under Mac OS X. Sigma Chess 6.1 also runs on the "Classic" Mac OS version 8.6 or 9.x (providing the CarbonLib extension is installed).
· Strong "multi-instance" Chess Engine
· Sigma Chess 6.1 can analyze multiple positions/games simultaneously by smoothly multitasking between each engine "instance". You can for example instruct Sigma Chess 6.1 to analyze one or more positions in the background, while you play a game in the frontmost game window.
· Position/Opening Line Database Search
· In Sigma Chess 6.1 Pro it is now possible to perform database searches on specific board positions and opening lines.
· Up to 1 Million Games in Collections
· Sigma Chess 5 Pro was limited to 32.000 games, but in Sigma Chess 6.1 Pro collections can contain up to 1 million games! (but obviously sorting and filtering is slower and uses a lot more memory for such large collections, so you might find it more practical to limit your collections to e.g. 100.000 games or less).
· Better PGN/EPD support
· PGN files can now be opened directly without you first having to create a new empty collection.
· HTML Export
· Sigma Chess 6.1 can now generate chess related web pages with embedded chess diagrams, annotation text etc (similar to printing). It uses the same piece set naming convention as in ChessBase, so you can use your favorite ChessBase piece sets instead of the standard Sigma Chess HTML piece set. Click here for an example, which shows how the included "Rules of Chess" collection/book looks when exported.
· Improved Position Library Support
· Now supports standard position classification glyphs (=, +/- etc). Also, you can now easily build your own position library by importing positions from game collections.
· Rating History Graph
· A new player ELO dialog is included which shows more rating statistics, including an ELO history graph showing the development of the player's ELO rating. In Sigma Chess 6.1 Lite only the results of the first 10 rated games are included.
· Multiple Board Sizes
· Sigma Chess 6.1 now supports multiple 2D board sizes.
· Custom Boards & Color Schemes
· You can now define you own custom color scheme and 2D board via the standard Apple Color Picker
· Easy and intuitive Clipboard Handling
· Copy/paste entire games/positions between game windows and collections.
· Many levels and time controls
· Including Monitor mode, Solver mode (limited by time and/or score ) and Fischer clocks.
· Full support for the ExaChess engine protocol
· The engine can thus be used from within ExaChess along with the other engines supported by ExaChess.


Limitations:

· As mentioned on the main page, Sigma Chess 6.1 Lite is freeware. Although it's a complete, full strength chess program and not just a demo, certain high end features of the commercial Sigma Chess 6.1 Pro version are either limited or disabled:
· The new position and opening line filters are only available for collections with at most 100 games.
· The new player rating history graph only shows the first 10 games.
· Collections can contain a maximum of 1000 games.
· Changes to opening/position libraries cannot be saved.
· Only the KQKR and KBNK endgame databases are included. The commercial Pro version contains several other 4-piece endings.
· Automatic game annotation/analysis are disabled for collections.
· Diagrams are not printed when printing collections/online chess books.
· Diagrams are not included when exporting collections/online chess books to HTML
· Transposition tables are limited to 10 MB, whereas the commercial version can handle transposition tables up to a size of 320 MB.
· At most three windows can be opened simultaneously.
· Monitor mode is not available.
· UCI engines are limited to max 64 MB transposition/hash tables.
· UCI engines cannot reduce the playing strength to a specific ELO setting.
· UCI engines cannot access Nalimov tablebases.

What's New in This Release: [ read full changelog ]

· Now bundled with the new HIARCS 12 engine!
· Fixed some stability issues.