Maigret collects a dossier on a person by username only, checking for accounts on a huge number of sites and gathering all the available information from web pages. No API keys required. Maigret is an easy-to-use and powerful fork of Sherlock.
Currently supported more than 2500 sites (full list), search is launched against 500 popular sites in descending order of popularity by default. Also supported checking of Tor sites, I2P sites, and domains (via DNS resolving).