Aquataxx is a version of the classic arcade and puzzle game “Ataxx,” which appeared in the game “The Seventh Guest” as “Microscope Game” among other places. It is (not always elegantly) written using Apple’s Cocoa frameworks entirely in Java, and should work on PowerPC and Intel machines as far back as Mac OS X 10.2.
You can play over the network, thanks to nimh.net.
Some people will have firewall issues because of the ports used and other nonsense that I decided not to work around since this is the last version of Aquataxx I’m supporting.
The full source code is included, and there was a MacTech article written about this game and some of the intricacies of programming in Java using Cocoa.