Angry IP Scanner (aka ipscan) is a free, fast, and easy-to-use network scanning utility that allows you to scan IP addresses, ports, and more. Portable version is also available.
Angry IP Scanner will quickly scan IP addresses and ports and has many other features like NetBIOS information (computer name, workgroup name, and currently logged in Windows user), preferred IP address ranges, web server detection, customizable openers, etc.
Angry IP Scanner is an excellent tool for network administrators or just inquisitive users wanting to stay informed about their network. It runs on Linux, Windows, and Mac OS X, possibly supporting other platforms as well.
Simple Port Forwarding works with webpages and not directly with your router making it a safe program to use. Supports 52 Languages and 2600+ routers. Portable version also available.