Impressive demonstration using the first mouse and graphics display by Douglas C. Engelbart in the year 1968(!)
Online Computer Museum
Computer Modell Katalog (German)
Computer-Archiv (German)
Computer-Museum München (German)
Homecomputer-Museum (German)
A lot of stuff about VAX, but also other historic machines and interesting projects (German)

DokuWiki, the system behind this website
Dev-C++, C++ development environment for Windows based on GCC
“Irrlicht”, a 3D engine
PuTTY, SSH client
WxWidgets, a class library for platform independent applications
GnuPG, a free implementation of PGP

The Wireworld Computer
“99 Bottles of Beer” implemented in (nearly) all known programming languages