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Avum vs Outlook Google Calendar Sync: Hosted Sync or a Free Desktop Tool?
Outlook Google Calendar Sync, usually called OGCS, is free, open-source software that copies events between Outlook and Google Calendar from a Windows computer. Avum is a hosted service: your rules run on Avum's servers, so calendars stay current when your laptop is closed, and you can add iCloud, CalDAV and ICS calendars alongside Google and Outlook.
Published by Avum. Product details were checked against the official OGCS project on November 2, 2026.
Avum vs OGCS at a glance
| Avum | OGCS | |
|---|---|---|
| Cost and operation | ||
| Price | From $5 / month | Free, donations welcome |
| Where sync runs | Avum's servers | Your Windows computer |
| Keeps syncing when your computer is off | Yes | No |
| Updates and maintenance | Handled by Avum | You install and update releases |
| Calendars | ||
| Google Calendar | Yes | Yes |
| Microsoft 365 and Outlook.com calendars | Yes | Through classic Outlook (v2) or Outlook Online (v3 alpha) |
| Works with the new Outlook app | Yes | Version 3, currently alpha |
| Local-only Outlook calendars stored on your PC | No | Version 2 |
| iCloud, CalDAV and ICS feeds | Yes | No |
| Several accounts in one setup | Up to 10 accounts | One Outlook and one Google calendar per profile |
| Control | ||
| Choose direction and copied fields | Yes | Yes |
| Filter by attendance, color, weekday, hour or date range | Yes | Partial |
| Combined calendar view with three time zones | Yes | No |
Sources: OGCS official site, OGCS quick start and Avum pricing. OGCS options vary by release; check the version you plan to use.
The real cost of “free”
OGCS costs nothing to download, and for the right person it is excellent value. The trade-off is that you become the operator. Sync only happens while the computer running it is on, signed in and connected. If you close your laptop on Friday and a client moves Monday's meeting over the weekend, your other calendar will not know until the laptop is back online.
You also choose the right release for your Outlook. The official project explains that version 2 needs classic Outlook, while version 3, offered as an alpha, adds an Outlook Online route for Microsoft 365 and the new Outlook. Alpha software is worth testing carefully before you rely on it for client meetings.
Avum's Sync Rules run on Avum's servers once your accounts are connected. Nothing has to stay running on your computer, and there is no software to update. You keep account access valid, and Avum handles the rest.
More than Google and Outlook
OGCS is built for exactly one pairing. Many schedules involve more: a personal iCloud calendar, a Fastmail or Nextcloud calendar over CalDAV, or a timetable or rota published as an ICS link. Avum connects all of these alongside Google and Outlook, up to ten accounts on the Premium plan, with no plan limit on the calendars inside each account. ICS feeds are read-only, so Avum copies their events into your writable calendars.
Avum Calendar then shows every connected calendar in one view with up to three time zones.
Privacy controls for work calendars
Both tools let you decide which fields travel. In Avum, each rule can replace the title with “Busy”, leave out the description and location, mark the copy busy or private, and filter which events are copied at all, for example only weekday events or only accepted meetings. Check the result in the destination with the busy-only copying checklist.
Whichever tool you use, check your employer's policy. A desktop utility and a hosted service both access calendar data.
Choose Avum if…
- Your calendars must stay current when your computer is off
- You use iCloud, CalDAV or ICS calendars as well
- You work on a Mac, a phone or several devices
- You would rather not install and update sync software
Choose OGCS if…
- You only need Google and Outlook
- A Windows PC with Outlook is running most of the day
- You are comfortable configuring and updating it yourself
- Paying nothing matters more than convenience
Moving from OGCS to Avum
Stop OGCS for the direction you are replacing before enabling the Avum rule, and identify the entries it created so you do not end up with two copies of each appointment. Switching sync tools without duplicates gives the cleanup order, and the sync test checklist helps you confirm the new setup.