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.
a good idea - 1 point. executed really, really well - 100 points.