It's not as supersweet as the old Res Rocket stuff, but it's still novel for cranking out ideas in a DAW over the Interweb. In a nutshell, it works like this:
- Load a [new] project in Reaper.
- Make sure you disable Options -> Preferences -> Audio -> Playback -> "Stop/loop playback at end of project"
- Add the ReaNinjam VST (which comes with Reaper) to your Master track
- Configure ReaNinjam to be in "Session Mode", and File -> Connect to one of the public session servers (it's like joining a chatroom)
- When you play your project, ReaNinjam transmits the audio you play to everyone else in the room, so when they play their project, they hear your stuff synchronized.
- Likewise, you'll hear theirs. So you can work together to record a song!
I really want to try skirmishing with this some day.