Erlang and online games
Taken verbatim from an email I sent to a programmer's mailing list I'm on:

I have decided that the only way for me to finally get around to
learning Erlang is to write a nontrivial project in it.  To this end, I
have decided to implement a multiplayer online game of some kind.

I'm only really interested in the Erlang backend, so I'm thinking a
text-based MUD of some kind that players can telnet to, but if someone
wants to write a graphical client or something that's also good.  A
frontend can be in any language/platform combination as long as I can
run it in Linux for testing.

I could probably do the whole backend thing myself given enough time,
but collaborators make things easier and more fun, especially to bounce
ideas off and discuss bits of code.  This is a learning project, so I'm
not expecting anyone to know Erlang at all before they join.

Also, people interested in the game design and worldbuilding aspect are
welcome to help out in just those areas without having to write any
code.