You can:
- Announce game ideas; mechanics or themes that you are exploring and wish to 'claim'.
- Dump ideas that you have thought of, but thought someone else would do a better job on.
- Request somebody make a game with a particular theme.
- Ask for ideas of what would make a good game.
- Brainstorm on ideas other people have had.
- Ask publically for help designing, balancing or GMing a game you have in mind.
- Discuss previously announced games or mechanics.
- Anything else constructive you can think of.
So yeah. There's lots you can do here.
Have fun!