By this I mean a group of musicians who will lay tracks for each other at very low or no cost.
It's not the sole purpose of HR, but that sort of thing definitely goes on here.
Probably more between friends than anything.
Also, share their music for critiuqe and appreciation?
That definitely goes in here. The MP3 mixing clinic is the place to be for critique and appreciation.
Can't have one without the other though.
How would such a group manage cross-platform recording?
Do you mean the logistics of file sharing?
I have a server that I upload to.
The site has a built in mp3 attachment system that I see people using.
A LOT of people use soundcloud in the clinic. The site allows soundcloud embedding with these tags (no spaces).
[ SOUNDCLOUD ] address here [ /SOUNDCLOUD ]
There are other filesharing systems like dropbox that are better suited to wavs etc.
The only thing to manage is the start point of your recordings. If you send me a stereo WAV of your song and ask me to record lead guitar, make sure you bounce your session from 0:00:00, or at least a known grid point.
I'll start my recording from the start of your wav, and then when I return it it's easy for you to line up.
Hope that's useful.