EIGRP

Except for the odd cisco class, I've never actually used EIGRP. It's another interior routing protocol, like OSPF and often used in place of it. It's cisco-only, as it's cisco's proprietary protocol, which makes it a non-starter in heterogeneous routing environments. (OSPF is based on standards and is supported by pretty much all vendors of "real" routers, which is to say "not a $30 home router for your dsl line".)

Unlike OSPF, EIGRP doesn't have the concept of "areas", so all of your internal network is lumped into a single monolithic administrative collective. Like OSPF, it establishes neighbor relationships with other routers and shares routes among its neighbors. EIGRP gives you a few more ways to tweak your routes, having bandwidth and delay instead of a simple cost metric and does route filtering a bit more granularly.