RANCID , by Shrubbery Networks , is a tool to retrieve network equipment (routers, switches, ...) configuration and put it under version control.
It provides archival and change detection over a wide range of vendors out-of-the-box, and can be extended to support more if needed using scripting (a combination of Perl and Expect is mainly used).
The system includes a web-based looking glass (which allows cached access to certain router commands via CGI).