Tiny Core Linux provides a basic graphical desktop in on 10 MB, making even Damn Small Linux look fat. Based on Linux 2.6 kernel, Busybox, Tiny X, Fltk, and Jwm, it is a minimal platform for building a custom desktop or specialized computing appliance that boots and runs quickly on modest hardware.

Extensions include development tools like the Gnu Compiler Collection, Python, and Ruby, but not Emacs, so you have to make do with Vim or another lightweight editor or do your own port. I may just have to install this on an old laptop to check it out.