The following software is no longer being maintained, but available here for those few who might still be interested in it. Some of it doesn't even run on Mac OS X, but requires Mac OS 9 or earlier. (Wow!)
This tool was useful in Mac OS X Leopard, versions 10.5.0 and 10.5.1. It fixed some annoying issues with the behaviour of Spaces on Mac OS X. Nowadays, Apple has fixed these issues themselves, and Triple-S is no longer necessary. Code and binaries are still available, however.
Universal Back Button keeps track of applications as they send URLs to each other, and offers you an easy way of going back to that application. For instance, opening a link in Mail will display that link in your browser. Hitting the Universal Back Button, located in your menubar, you are instantly taken back to Mail. Universal Back Button is free and open source. Please read this blog-post for information on how to get Universal Back Button working on Mac OS X 10.6.5 and later.
Some blasts from the past. If you click through to the product pages, you'll see them just as they appeared back in the day. Enjoy! You can find the whole range of software here.
Super Othello is an implementation of the classic board-game Othello/Reversi.