I haven't seen this thread yet, so I'm creating one. If you're not familiar with it, every year we do 4-people collaborations using 4-track cassette recorders. Each person records a single track, and then sends the tape to the next person by mail, until the last person records their part, mixes the song, and uploads it to the site.
If you have access to a 4-track you should give it a try, it's incredibly fun! Just make sure it supports normal speed, not double.