Linux, one way or another, really brings out your inner hacker. I've been tinkering quite a bit with DeLicate Linux. It's a lightweight distro made for old computers that uses the 2.4 kernel. Right now, I have DeLicate running on a Pentium 166 with 64MB of RAM. Surprisingly, Fluxbox and Xchat run without any huge problems. Replacing Bash with Dash helped free up some RAM as well. DeLicate uses pacman as the package manager, so building new packages is as easy as creating a PKGBUILD file.

I have also set up a DeLicate package repsitory and a Git repository for the PKGBUILD files.  So if you have an old Pentium laying around, go fire it up and check out DeLicate. There's an active community too.