Today the Google wave team released an open source version of their software. It's Java 6; OS X users will have to take a chance with the recent buggy Java release from Apple. (I have to back up my machine before I take that jump - I didn't expect to take upgrade as there's a developer preview of the _next_ one waiting in the wings. )
It's not exactly what Wave itself is - for example it does not have a persistent store, doesn't implement the same type of user, and uses a funky stand-alone terminal ( think pine ) client. It does do the XMPP server federation stuff to talk back and forth between different deployments stuff. It does log tons of stuff; the stack of signing and transformations, etc. And you can bop around in the ASCII chat like wave tool with your unauthenticated friends. Just don't expect to point your browser at it and get the wave experience.
It's being released as a playground for integrators and as an executible protocol testbed. Expect rapid deltas to the code. They are hosting 2 servers for you to test your integration.
They gave a demo of 2 federated wave servers and 3 end users doing an ASCII wave.
You can find it in a mercurial version control system at http://code.google.com/p/wave-protocol/source
They really want us to all come play with them.
Best quote of the day: "We built an innovative cool system which we expect to be abused in innovative cool ways..."