PeerGuardian 2

300px-Peerguardian2.jpg Ever used Black Ice Defender? That would be a ip blocker for Windows that is used to block incoming IP addresses that could or could not be malicious to your system. What’s interesting is that not only is this open source, but it’s been ported to MacOSX, linux, and Windows.
Pretty useful when it comes to blocking harassing IPs. Another great feature is that Phoenix Labs actually has a compilation lists of IPs of P2P blocking, adware, malware, educational IPs, government IPs and other types of lists. These lists can be set up to be cached straight into PeerGuardian so that you know exactly who is allowed and who isn’t onto your system.
Think of this as a software firewall. Which it is on a pretty preliminary scale. It’s technically an IP/port blocker. Version 2 is written in C++ and uses less resources than the first version (Visual Basic) and was written to by different developers. There is also a Lite version if you don’t need the fancy pants GUI.