[Open-access] [OT] bibliography sharing?

[Tom Roche]

Dunno if this is OT for this group, but ... has anyone done a brief
howto or guide to bibliography/citation sharing? Mendeley is probably
the obvious option, but there are other (and IIUC freer) mechanisms,
e.g., Zotero groups

http://www.zotero.org/groups/browse

but I'm guessing (knowing little in this space) there are more.

apologies if there's a better channel for this question,
otherwise TIA, Tom Roche <Tom_Roche at pobox.com>