Maltego!

poortego - Open-source ruby project to handle the storage and linking of open-source intelligence (ala Maltego, but free as in beer and not tied to a specific / proprietary datbase)

Netglub, the really open source information gathering solution.

Visallo helps intelligence analysts, law enforcement detectives, and fraud investigators produce more rigorous and defensible conclusions by helping them discover, visualize, and understand complex relationships hidden in massive amounts of data. It's an all-in-one suite of easy-to-use, web-based, visualization tools and machine learning data analysis algorithms that augment an investigator’s hard-earned experience and intuition with data-driven insights that would be difficult, if not impossible, to discover otherwise. »