"The MacPorts Project is an open-source community initiative to design an easy-to-use system for compiling, installing, and upgrading either command-line, X11 or Aqua based open-source software on the Mac OS X operating system."

Free Mac software for taking webpage screenshots. Can capture the entire length of a page (beyond the "fold").

"HandBrake is an open-source, GPL-licensed, multiplatform, multithreaded DVD to MPEG-4 converter, available for MacOS X, Linux and Windows."

Some very useful utilities. Service Scrubber helps you manage OS X services, Witch turns command+tab into something that can access the windows of individual applications, not just the applications themselves.