Open source network mapping utility that provides security scanning and network discovery.
Free opensource software built into many OS
Pros: The price is right and it does a lot while only consuming a little resources. Useful for network scanning and penetration information gathering.
Pros: Works great, is open source so no the usual open source stuff- community supported etc. It provides network mapping for your enterprise
Cons: learning curve is steep. Community support is good, but is not always fast when you are in a time crunch.