Linkurious - Search and visualize your graph data through a simple web-based interface
Lampyre - Lampyre - an efficient data analysis and OSINT multi-tool for everyone.
SIREN.io - Siren is an investigative intelligence platform.
Gephi - Gephi is an open-source software for visualizing and analyzing large networks graphs.
Netglub - Netglub, the really open source information gathering solution.
Maltego - Maltego is an open source intelligence and forensics application.