RANCID monitors a router's (or more generally a device's) configuration, including software and hardware (cards, serial numbers, etc) and uses CVS (Concurrent Version System), Subversion or Git to maintain history of changes.
Rancid currently supports Allied Telesis switches running AW+, Cisco routers, Juniper routers, Catalyst switches, Foundry switches (now Brocade), Redback NASs, ADC EZT3 muxes, MRTd (and thus likely IRRd), Alteon switches, and HP Procurve switches and a host of others.