fink.sourceforge.net
It is the greatest asset to Mac OS X power users. It is a realatively simple way to install just about any application that comes with a standard Linux distribution. X-Windows (via X Darwin), Ethereal, Emacs, vi, orbit, mysql, gnome, kde, gpg, mutt, elm, gzip
Many of them are command line applications, but the X Darwin is sweet. It will let you run XWindows in "rootless" mode, where you can have an Aqua windows and a gnome or KDE window on the same screen. Plus it works great with multiple monitors.
One cool trick I do... I have a Linux box at work. It is running VMWare for Linux. I have Windows XP installed as a Virtual Machine (think Virtual PC, but much faster, does not emulate a PC as much, since there is a real PC to work with).
On the linux box, I do:
Then I "setenv DISPLAY my.dns.name"
Then I do "vmware &" and up on my Mac, a new window pops up. It is the screen of a virtual windows XP box that actually runs pretty damn fast. The only thing that is going back and forth over the network is the screen updates and keyboard, mouse, and sound.
There is another program, called VNC that does the same for just about any platform. (no ****, it can run client and server on just about anything) My friend runs the VNC server on his Mac Server, and runs the client on his pocket PC with a wireless card. He can control the mac from the pocket PC. Sick but true.
BTW, vnc comes with Fink.
If you try it, make sure you read the directions to install it. You download one thing, and install it in the familiar mac os package method, but then you need to do the rest of the install in a terminal window.