A website that can extract many different sorts of information pertaining to IP addresses and networks, least of all querying several dozen blacklists to see if an address has been flagged as a spammer's.
A realtime strategy game in which you compete in a virtual space with others to build the biggest, most robust network you can while attempting to compromise or crash the networks of rival system admins. It sounds a little like Starcraft meets Neuromancer with a healthy dose of the movie Hackers thrown in for fun. Runs on Windows as well as Linux.
OONI is a project for collecting and analyzing data pertaining to Internet censorship and surveillance around the world. The project aims to determine and chart just what measures are in place where and how effective they are.
Their source code reside in a Git repository at torproject.org.