Q1: OpenView NNM, Unicenter NMS and Tivoli NetView as framework-components. More standalone heavyweights: Aprisma Spectrum, Concord Network Health to name a few.
However there are a lot of cheaper ones around, sometimes enough for what you need. E.g. IpSwitch WhatsUp Gold is very popular, and only about USD 300-500. OView and UC start at USD 10,000 per console and sometimes also caps for managed nodes.
Q2: Not very much in terms of functionality. Their architectures do differ, UC is a bit more modern but OView has a lot of extra add-ons merged over the last few years - e.g. RiverSoft layer2-technology.
HTH,
- The Netherlands