Tonido Sync (http://www.tonido.com/app_sync_home.html) provides the same private, local sync like AeroFS. the Tonido solution is very mature and it also has mobile apps for all the popular mobile OSes (iOS,Android, Blackberry and Windows 7.5)
When it become not acceptable to charge money for a software service. Tonido is a mature offering and works. Customers are ready to pay money for its worth. I would rather choose a software that will charge money for it rather than a free one.
