Bitbucket is a web-based hosting service for projects that use either the Mercurial (since launch) or Git (since October 2011) revision control systems. Bitbucket offers both commercial plans and free accounts. It offers free accounts with an unlimited number of private repositories (which can have up to five users in the case of free accounts) as of September 2010, but by inviting three users to join Bitbucket, three more users can be added, for eight users in total.