You can copy, modify, and redistribute the source code, under the GNU GPL of course. It also has credits for the people who made suggestions and bugfixes.
This is not an product of Set Enterprises. In fact, they sent me a very polite letter about it, so I've gone ahead and removed all of their copyrightable material, leaving only the base game. That's why the colors, patterns, and shapes may be a little different than you're probably used to.
To play, click on your player button, then click 3 cards that you think might be a gropu. Don't worry if you mess up - just try another 3. The cheat button marks three cards that make up a group - I wouldn't recommend using it in games with your friends :). Try the "help" button for rules. If you're alone, try single player mode.
I play with these settings and win about half the time.