Keeper is an open-source calendar syncing tool that can be used to sync the blocks of time marked as "busy" on your personal, work, business and school calendars.




Spanning Sync is described as '3 is the one app that syncs both iCal with Google Calendar and Address Book with Google Contacts. It gives you even better control over how your information syncs, and is now up to 10x faster!' and is an app in the office & productivity category. There are six alternatives to Spanning Sync for Windows, Web-based, Microsoft Outlook, SaaS and Mac. The best Spanning Sync alternative is Keeper, which is both free and Open Source. Other great apps like Spanning Sync are SyncThemCalendars, SYNCING.NET, OLContactSync and SyncMate.
Keeper is an open-source calendar syncing tool that can be used to sync the blocks of time marked as "busy" on your personal, work, business and school calendars.




SyncThemCalendars allows you to block time in one calendar based on events in another calendar.
SYNCING.NET offers powerful Data and Outlook synchronization for individuals, professionals and businesses. By providing secure PC synchronization, integrated file and Outlook sharing, users can access all their data at any time and any place.
OLContactSync allows you to easily synchronize your Outlook contacts with any other Outlook user’s contacts per E-Mail for free.

SyncMate syncs data on Mac with Android and iOS devices, Windows services (Outlook, Office 365 Business and Office 365 Home accounts), other Macs, Google, Dropbox and iCloud accounts, any mounted storage devices, MTP devices.


Synchronize any Microsoft® Outlook® folder with anyone elses (except Drafts, Outbox, Sent Items and Deleted Items). The folders you allow to be synchronized will do so in the background by e-mail.