SpiderFoot is an open source intelligence automation tool. Its goal is to automate the process of gathering intelligence about a given target, which may be an IP address, domain name, hostname or network subnet.
SpiderFoot can be used offensively, i.e. as part of a black-box penetration test to gather information about the target or defensively to identify what information your organisation is freely providing for attackers to use against you.
Read more at the project website: http://www.spiderfoot.net