Flock Sync is described as 'Flock syncs your contacts and calendars between multiple devices while protecting your privacy with strong encryption' and is an app in the Backup & Sync category. There are four alternatives to Flock Sync for a variety of platforms, including Android, Windows, Android Tablet, F-Droid and iPhone. The best alternative is EteSync. It's not free, so if you're looking for a free alternative, you could try Android Sync Manager WiFi. Other great apps like Flock Sync are DAVx5 (Paid, Open Source) and BirdieSync (Paid).
Sync your contacts, calendars and tasks. Two-way sync: Manage and synchronize address books, calendars and task lists with a single app. Secure & reliable: Designed for simplicity, security and privacy. Modern GUI.
Android Manager WiFi lets you sync your Android phone with your PC over WiFi. With Android Manager, you can manage, sync, and back up your contacts, messages, photos, video, music, applications and calendar.