Brutus is one of the most popular Bruteforce password cracker. It is used to find out HTTP, POP3, FTP and Telnet servers' passwords. It can simultaneously build 60 connections. One can extend this tool with plugins. Facilitate dictionary based user/password attacks against various network applications. from the doc: 'It is a remote interactive authentication agent. Brutus is used to recover valid access tokens (usually a username and password) for a given target system. Examples of a supported target system might be an FTP server, a password protected web page, a router console a POP3 server etc.'