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Outlook Google Calendar Sync vs OneCal: catalog facts
Outlook Google Calendar Sync	OneCal
Free Free and open source under MPL-2.0, supported by donations.	Freemium Free to start with no credit card required.
Windows	Android, iOS, Web
Syncs attendees, reminders and descriptions Portable version needs no installation	Real-time sync across Google, Outlook and iCloud Control over which event details are copied
Windows only and needs desktop Outlook Requires a Google account	Requires granting a third-party service access to your calendars Hosted only, with no self-hosted option
Downloadable app	Downloadable app, Hosted service
Open source	Closed source
License: MPL-2.0	License not stated
Account needed	Account needed
Needs internet	Not stated if it works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked October 2, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.