Maltego is an intelligence gathering programme that can be used to identify relationships and real world links between people, groups, companies, organisations, phrases, IP addresses or other entities. These identities are linked using open source intelligence, which is that the information is gathered from publically available sources. Whether it's the relationship between your bank and other companies, or you want to analyse the network of the countries belonging to NATO and their links with the rest of the world, Maltego can locate, aggregate and visualise your network data. All with an easy to use front-end interface. This tool is not open-source. However, you can download the community version of Maltego for free (not for commercial use).