OggSync is described as '’s mission is to keep mobile users in sync with the scheduling demands of a busy lifestyle, keeping all calendars in one manageable view!' and is an app in the Backup & Sync category. There are more than 10 alternatives to OggSync for a variety of platforms, including Windows, Android, Online / Web-based, Android Tablet and iPhone. The best alternative is EteSync. It's not free, so if you're looking for a free alternative, you could try PhoneCopy or Outlook Google Calendar Sync. Other great apps like OggSync are DAVx5 (Paid, Open Source), AkrutoSync (Paid), Outlook CalDav Synchronizer (Free, Open Source) and GO Contact Sync Mod (Free, Open Source).
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.
PhoneCopy is the easiest way to backup, manage, and synchronize personal data from a mobile phone to the cloud. Phonecopy securely manages phonebook contacts, calendar events, SMS messages, photos, and videos. All data are accessible via a web browser.
Free Outlook Plugin, which synchronizes events, tasks and contacts between Outlook and Google, SOGo, Horde or any other CalDAV or CardDAV server. Supported Outlook versions are 2016, 2013, 2010 and 2007.
GO Contact Sync Mod is an open source tool to synchronize your Microsoft Outlook contacts with Google Mail. With this tool you do not need to enter your contact details more than once, always have the latest version everywhere: in Outlook and in Google.