IP Scanner - Angry IP Scanner

Angry IP Scanner is a fast and friendly network scanner.
Thats what THEY say.
They also say that Angry IP Scanner (or simply ipscan) is an open-source and cross-platform network scanner designed to be fast and simple to use. It scans IP addresses and ports as well as has many other features.

It runs on Windows, OsX and Linux.

Get it here:

http://www.angryip.org/w/Download