You form an alliance by sending an allies add command, like this:

allies add 5

This will offer the Privateers (player 5) an alliance. To confirm the alliance, the Privateers must have to send the same command, with your race number. If you are Birds (player 3), he has to write

allies add 3

To revoke an alliance, or take back an offer, you send an allies drop command:

allies drop 5
This is a testing version.
It may be incomplete, and have more bugs (or features) than the public live version at planetscentral.com.