Re my post last night about server-less file sharing, a friend writes:
I made good use of Eudora for this. It has does file sharing through servers, but unlike Groove, was asynchronous and runs on both the Mac and Windows.
Basically, you set up an email account for each person who wants to share folders. Then you go into Eudora and add an ESP folder, and invite the other Eudora users (the free version works, so just tell your friends to download it). The interaction is straightforward.
Turns out this has been available in Eudora since 2000!