Metasploit is an open source exploitation framework that acts as a tool for developing and executing exploit code against a remote target machine
The Metasploit Framework is an open-source project owned/sponsored by Rapid7 for vulnerability assessment, exploitation development, penetration testing, and many other computer and network security-related tasks.
Since version 3 of the Framework, Metasploit has been written primarily in Ruby. Version 2 and older were written in Perl. The various payloads, stagers, and shellcodes are primarily written in C, assembly, and Java.
Metasploit is developed on Github. Documentation and community forums are available on Rapid7's community site. Questions can also be asked in the #metasploit channel on Freenode.