This service uses a Free microblogging tool called GNU social. GNU social is available under the GNU Affero General Public License Version 3.0, a Free Software license for network services.
You can get a copy of the software by following links from the GNU social main site¹. The version of the software that runs on this site is unmodified from that version. The site also depends on certain libraries and other software; these are all bundled in the GNU social repository² and release archive files.