They are FolderShare for Macs, a little bit nicer and at a time where more people "get" the need.
Fun Historical note: FolderShare was founded 10 years before DropBox. MSFT paid to acquire FolderShare and then squashed all of the good things about it out of the project.
"...and at a time where more people 'get' the need."
I think this is a really good point. The market-timing was right for dropbox. More people with multiple machines (mostly laptops) so the desire to backup/sync across devices became more important.
Fun Historical note: FolderShare was founded 10 years before DropBox. MSFT paid to acquire FolderShare and then squashed all of the good things about it out of the project.
http://www.microsoft.com/presspass/press/2005/nov05/11-03Fol...
Second-mover (or N-mover) advantage and clean execution is undervalued, IMHO.