Google Contacts, Free Address Book, Contacts+ , Kylook, Clearbit Connect, Microsoft People, Memotoo, Kontact - KAddressBook, Covve Personal CRM, GlipMe, Discoverly, Ampliz Sales Buddy, Windows Contacts, fruux, Marcom Robot Data Enrichment Engine, Junkyard Panda, CloudvCard, O-Sync, OLContactSync, Relationship, AddressBookSync, Addza, Leadfly, Ark browser plugin, Adsuisse, Contacts Express, Soocial are some alternatives to CircleBack.