In addition to the Audio module, which I feel will streamline a lot of things we do here, as well as open up new avenues for sharing and collaboration, I've also deployed the Track 'n' Stack module (official site), which extends Audio to facilitate working collaboratively on audio projects. I've only started to experiment with this module, so I'm posting what I've figured out so far, but there might be some confusion on my part, so feel free to add to the discussion if I'm wrong about something.
I've started a demo Track 'n' Stack project here, which can be used for experimenting: http://bassplaying.com/?q=node/1035
Track 'n' Stack adds an option group, labeled "Collaboration," to any Audio mode that you create. There are two checkboxes: "allow others to collaborate" and "checkin approval." Checking the first option allows others to contribute to your project (essentially, this turns the regular Audio node into a Track 'n' Stack Audio node). Once you allow this option, other users will be allowed to check out your file, signaling that they want exclusive access to the file in order to remix it or add an additional track to the project. The file you used to start the project will be listed as File1.mp3. It's also the one that will be played by the embedded Flash player.
When they're done editing, they check the file back in, relinquishing the exclusive access, and creating File2.mp3 in the list of project files. There's a site-side setting for expiring their lock on the file if they check it out but never check it back in (default is three days, one week is max). In fact, to keep things on separate tracks, the user can check in up to three files (maybe two separate tracks and a sample sub-mix?). If you have "checkin approval" checked, you'll get to review the file(s) and accept or reject it/them. If this option is unchecked, the file(s) gets added to the project automatically, which isn't a bad way of doing things and might work well for us, depending upon the nature of the musical project. There's an email notification to the project owner upon checkin. And there's an email notification to the contributor upon checkin approval.
The idea here, I think, is for the owner of the project (i.e. the person who created the original Track 'n' Stack mode) to create sub-mixes of the contributed files and replace the Audio file of the node with the most recent sub-mix. I haven't done it that way in my demo. I had the contributor do his own sub-mix and post it (as File2.mp3), but I don't think that's the best workflow. I think it's better to add your tracks separately, providing a scratch sub-mix for the owner's benefit (as there can be timing issues, especially when using compressed file formats).
Anyway. This will be the first of many experiments. Feel free to create your own. I look forward to remixing things and contributing tracks to your projects. And I'm sure Paul is already thinking of a way in which we can use this for the next BassIAB project. :)
You'll notice that Track 'n' Stack adds a submenu to Audio (in the left-hand navigation section) called "Browse in progress." This is where you will find all Audio nodes that currently have collaboration enabled. Note, also, that you have to click the title of the node itself to see all the files in the project. The "teaser" just shows you the Flash player and whatever file it contains (e.g. the first track, a sub-mix, etc.).
Once a project is done, I guess you just edit the node and uncheck the collaboration options and it falls back in with the other audio nodes (grouped under the Audio link).