Multi Player is a networking tool for gamers. It allows you to link your Steam account to import your game library, and then you can find other users or groups that are centered around games that you own! At its core, Multi Player is a chat application that allows both private messaging between users you are friends with and group messaging with members of groups centered around different games.
Note that the server is hosted on Heroku so your first Login or Register attempt will fail and will merely cause the server to spin up. Wait a few seconds and then try again.
Also be aware that if you intend to link your Steam account, you will need your browser set up to allow third-party cookies. This is due to the client redirecting to the server, which in turn redirects to Steam.
If you do not have a Steam account (or don't want to sign up with your own), you can use the test account that is pre-linked to a Steam account. The test account has the following information: