Features like "Chess online", "uno", "trivia" or any typical/similar online games you can have between ambrosia members. Or create a nice client, to where you can play and invite friends via client (Not like Steam, IRC, TS3). A more advanced chat-program/feature where you can add friends. Have a lobby room where you see whoever are online in ambrosia forum/or client, will be able to read or play from there. For example arrange some wars/mixes with those you find online then and there, or do other things - faster.
[Also... Is there a way I can get this forums theme/background in color WHITE? If not, may I suggest you add this, or make it permanent?]