Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
TCPView - TCPView is a Windows program that will show you detailed listings of all TCP and UDP endpoints on...
Eusing Free IP Scanner - Free IP Scanner: a very fast IP scanner and port scanner.
TcpView For Linux - TcpView For Linux. Touch screen friendly design graphical network connections viewer for Linux.
Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use
MASSCAN - This is the fastest Internet port scanner.