XORP is an open source IP router that can run on PC hardware. Enterprise-class routers from Cisco and other routher manufacturers have been highly priced and are often administered by high-priced people who typically barricade their knowledge from the rest of the IT staff.
This Business Week magazine article considers the threat to Cisco that is posed by XORP.
Open source has been sweeping the IT industry. Operating systems, databases, and application servers all have several viable open source products. Products in the networking layer of the IP stack still have fat margins and over-priced personnel and support. This stronghold of fat margins is now under seige by open source.