Kontact
Open Source
Kontact is a personal information manager and groupware software suite developed by KDE. It supports calendars, contacts, notes, to-do lists, news, and email.
fruux
Freemium
fruux is a cross-platform synchronization service.
Memotoo
Commercial
Memotoo sync all your contacts from Gmail, Facebook, phone, Thunderbird, Outlook, etc in a single address book.
Compare Google Contacts with alternatives
Compare Kontact and Google Contacts and decide which is most suitable for you.
Compare Memotoo and Google Contacts and decide which is most suitable for you.
Compare fruux and Google Contacts and decide which is most suitable for you.