"...le jeu de l'harmonie universelle"

Play Othello on Macintosh

Use Cassio to play the game of Othello against the program. Review and analyze games. Browse through the WThor database for instant access to 90000 tournament games. Practice your endgame skills by solving graduated puzzles... Cassio is a powerful, simple, fast othello board for Mac OS X. Like so many world champions, use a Mac to play Othello!

Othello board
Fig. 1: An Othello game. (Larger image, 170kB)

All features
Fig. 2: Beautiful graphics. (Larger image, 47kB)

News - October 6th, 2017

  • Version 8.4 of Cassio is available (Intel only)
  • Latest version, works from Mac OS X 10.3 to Mac OS 10.12...
  • This is a stable release which focuses on performance and quality of play: Bruno Causse and Richard Delorme have joined the programming team and provided two high-level "othello engines" (Roxane and Edax, respectively) which communicate with Cassio for analysing moves. See the page about the othello engine protocol for details, or download the new Cassio archive to get Cassio with the engines.

News - November 6th, 2012

  • Version 7.8 of Cassio is available (Intel only)
  • Brings nicer graphics for the evaluation curve and the PDF export, along with the usual bug fixes and small performance improvements...

Older news - August 11th, 2009

  • Version 7.5 of Cassio is available (Intel and PowerPC)
  • This is a stable release which focuses on cleaning and modernizing the interface, and offers the usual speed improvements in the play : version 7.5 is up to 5 times as fast as the previous versions. Other notable new features include high-quality graphics (for both 2D and 3D boards) and a nice, shiny cloud view of the quality of the games in your databases.

Learn more about Cassio



Features of Cassio include:

All features

Fig. 3: A complete othello framework. (Larger image, 390kB)


Cassio can be downloaded from this server as a self-mounting archive (.sit).

Installation instructions for Cassio:

  1. Choose one of the versions in the following tables, download the archive (the archive should decompress automatically)
  2. Copy the whole "Cassio folder" in your Application folder (I insist: you must copy the whole enclosing folder, not only "")
  3. Double-click on the Cassio application inside its folder
  4. If necessary, say "Open anyway" to the warning saying that this application was downloaded from the Web, do you want to open it anyway?
  5. If necessary, open your System Preference Panel for "Security & Privacy", and say "Open anyway" to the sentence saying that this application was downloaded from the Web, do you want to open it anyway?
Note: steps 4 and 5 are necessary since Apple have strengthened their security rules and do not allow unsigned applications from sources outside the AppStore to be run by default on newer Macs.
I do not distribute Cassio via the AppStore because I don't want to pay Apple 99 dollars a year just to buy the right to sign my application. If you trust me, you trust me.
If you are stuck with steps 4 and 5, see for some advices about this subject.

Stable version of Cassio (8.4) in French (for Intel) .sit file Cassio_francais.sit (192 MB)
Stable version of Cassio (8.4) in English (for Intel) .sit file Cassio_english.sit (192 MB)

Stable version of Cassio (7.5) in French (for PowerPC) .sit file Cassio_francais.sit (154 MB)
Stable version of Cassio (7.5) in English (for PowerPC) .sit file Cassio_english.sit (154 MB)

Once you have installed one of the stable versions above, you may want to experiment with the latest development version, which is available in the directory below, along with the source code. Note that, to reduce bandwidth, only the interface is included in the archives of the development directory (no documentation, no database, no graphics, no engine, etc.), so if you are new to Cassio, you have to download one of the stable releases first.

Latest development version: .dmg file See this directory and the version history.
Source code: .dmg file (3.9 MB). In Pascal, C and ObjectiveC, needs Xcode 3.0 and CodeWarrior 8.3 or better

License and Feedback

Cassio is distributed as shareware (15 euros), with its source code available free of charge (source code in Pascal, 3.3MB). Note however that no feature is disabled in Cassio if you don't pay the shareware fee, and that there is *no* painful reminder dialog, either. In that context, shareware means honor : if you like Cassio, please consider paying it.

Cassio is copyrighted work: Copyright (c) 1992-2018, Stéphane Nicolet. All rights reserved. Permission must be obtained for commercial redistribution.

Like any author, I enjoy feedback on my work. For any question, suggestion, or problem report, please write an e-mail to, or send me a postcard at Stéphane Nicolet, 24 rue Titon, 75011 Paris, France.

Mailing List

A mailing list for Cassio users is available. New releases will be announced on this list. To subscribe, send this email.

Frequently asked questions

Where does the name "Cassio" come from?
From Shakespeare : while almost everybody remember the names of the three best-known characters of the famous Shakespeare tragedy, Othello (the noble Moor), Desdemona (Othello's beautiful wife) and Iago (the villain), relatively few people seem to be able to name Othello's faithful, naive and, it has to be admitted, slightly stupid lieutenant of the Venetian general: Michael Cassio.

How strong is the program?
Very very strong. I know what I mean : I've been othello vice world-champion in 1996 and 2007, and the program consistently beats me :-) In fact, Bruno Causse, Richard Delorme and myself have been refining Cassio's othello engine for more than 15 years now, using the best artificial intelligence techniques known to us. The program has won several tournaments (both human vs. computer and computer vs. computer tournaments), and is competitive with the top programs running on PC and UNIX platforms.

Hasn't Othello been solved?
Short answer : No.
Long answer : It is true that the best programs now surpass the very best humans, but nobody has solved Othello in the mathematical sense yet. This strength doesn't prevent humans beings from enjoying playing the game, including in competitive play (National championships, World Championships, etc.) In that respect, the situation for Othello is similar to Chess, where the best programs beat 99.99% of competition players. If you want to know more about Othello, please find and visit the site of your local Othello association! A good starting point is the web site of the French Federation of Othello.

How can I pay the shareware fee?
Cassio is distributed as 15 euros shareware, with its source code available free of charge. If you like and use Cassio, please consider paying for it. The easiest way to pay for Cassio is by postal mail : just send me a postcard or a small written word, with 15 euros in the envelop, at the following address : Stéphane Nicolet, 24 rue Titon, 75011 Paris, FRANCE. Thanks!

Does or will Cassio run on Mac OS X, 9, 8 ... ? On PowerPC and Intel processors?
Yes, Cassio is a so-called Carbon application, and should run fine from System 8.6 upwards, but it is optimized for Mac OS X and Intel processors. For the time being, a PowerPC compile of the lastest vesrion of Cassio is still available, of course. Older versions, running on systems as old as System 7, can be found in this directory (try the "old_Cassio" files).