vmm is the easy to use and configurable command line tool for administrators and postmasters, to manage domains, alias-domains, accounts and relocated mail users. See the Features of vmm page for more details. It allows the fast and easy management of mail servers.
The most current version of vmm is 0.6.2, released on 01 February 2014. Older releases are listed in the Release history of vmm.
In short: “New BSD License” aka “3-clause license”. For a few more details see the COPYING file.