Arcanist is the command-line tool for Phabricator. It allows you to interact with Phabricator installs to send code for review, download patches, transfer files, view status, make API calls, and various other things. You can read more in the User Guide
For more information about Phabricator, see http://phabricator.org/.
Arcanist is released under the Apache 2.0 license except as otherwise noted.