OGCS: Probably the Best Free Tool for Outlook ↔ Google — With One Catch
Ask ChatGPT or Claude how to sync Outlook with Google Calendar and one name comes up almost every time: Outlook Google Calendar Sync, or OGCS. Deservedly so. Paul Woolcock’s open-source project has been around for many years, is actively developed, and does exactly one thing very well: keeping classic Outlook desktop and Google Calendar in sync — for free.
Let’s be upfront: OGCS is a very good tool — for a clearly defined niche. If you’re technically inclined, run classic Outlook desktop on a Windows PC that’s on most of the time anyway, and deliberately want a free local tool, OGCS will make you happy. For most other setups — Mac, phone, “New Outlook”, multiple devices, a computer that’s sometimes off — a server-side sync is the better choice. The honest comparison below shows why.
What OGCS Does Well
OGCS is a small Windows program that runs alongside Outlook — in the system tray, even portable without installation if you prefer (e.g. from a USB stick). For a free tool, the feature set is remarkable:
- One-way and two-way sync between Outlook and Google Calendar
- Full event details: subject, description, location, attendees, reminders, availability, private flag, and even categories/colors
- Differential updates — only changed attributes are transferred
- Scheduled sync plus push sync the moment something changes in Outlook
- Free and open source — funded through voluntary donations
The project is very much alive: the current v3 alpha shipped in July 2026, and the GitHub repository has over 2,000 stars. OGCS is not an abandoned hobby project — it’s well-maintained software.
Requirements: Windows with .NET Framework and classic Outlook desktop (versions 2003 through 2024 plus Microsoft 365 desktop are supported). For “New Outlook” there’s a v3 alpha since 2026 that works through the cloud interface — but it’s explicitly alpha software; the stable v2 line requires classic Outlook and entered maintenance mode in February 2026.
The Structural Limits of OGCS
None of this is a bug or sloppy work by the developers. These are consequences of the architecture: OGCS runs locally on one Windows PC.
1. PC off = sync off. OGCS only syncs while your PC is running and the program is active. Machine asleep or shut down: the sync stands still. Add an event from your phone to Google while you’re out, and it won’t reach Outlook until your machine boots up again. On vacation, over the weekend, after hours: no sync. If you rely on free/busy blockers to prevent double bookings, that leaves a time-window gap — exactly when other people are booking you.
2. One machine = one sync node. Windows only. The configuration lives on exactly one machine — your entire calendar sync depends on that single PC. Mac users are out entirely. If you only use Outlook in the browser (“New Outlook” or web-only M365 licenses without desktop apps), the stable version won’t work for you at all. And updates and configuration are on you — it’s software you operate, not a service that runs for you.
3. Full details by default. OGCS copies events completely — including attendees and descriptions. Often that’s exactly what you want, but for separating private and work calendars it’s exactly wrong: your employer doesn’t need to read that Thursday says “couples therapy” in your personal calendar. There are no granular visibility levels per sync.
4. Setup is doable, but not a two-minute job. Authorize your Google account, pick calendar pairs, configure sync direction and attributes — with some care it’s done in 15–30 minutes, but you should know what you’re doing.
OGCS vs. Kalender Sync at a Glance
| OGCS | Kalender Sync | |
|---|---|---|
| Price | Free (donations) | Free plan (1 sync), Basic from €4/month |
| Runs | Locally on your Windows PC | Server-side, 24/7, device-independent |
| Syncs while PC is off | No | Yes |
| Operating system | Windows only | Any (works via cloud APIs) |
| Outlook flavor | Classic Outlook desktop (New Outlook only via v3 alpha) | Any — including web-only and Mac |
| Supported providers | 2 (Outlook ↔ Google) | 9 (Google, Outlook/M365, Apple iCloud, GMX, WEB.DE, mailbox.org, Infomaniak kSuite, CalDAV, iCal feeds) |
| Detail level | Full details (configurable per attribute) | Selectable per sync: busy only · title + time · full details |
| Two-way sync | Yes | Yes |
| Setup | ~15–30 minutes, Windows program | ~2 minutes, no installation |
| Privacy | Data stays local + with Google/Microsoft | GDPR, hosted in Germany (Hetzner), DPA for business |
One row deserves special attention: provider breadth. OGCS handles exactly two providers — Outlook and Google. Kalender Sync connects 9 provider types and is the only tool in this comparison that also supports the German providers GMX and WEB.DE. If an iCloud calendar, a GMX mailbox, or a Nextcloud CalDAV joins the mix later, you won’t need a second tool.
One genuinely fair point for OGCS: because it runs locally, there is no third-party server processing your events. If that’s your top criterion and the limits above don’t affect you, OGCS is strong on privacy.
Our Verdict: Which Tool for Whom?
OGCS is the right choice for a clearly defined niche: you’re technically inclined, use classic Outlook desktop on a Windows PC that’s (almost) always on, have exactly one calendar pair (Outlook ↔ Google), want full event details transferred, want to spend €0 — and no third party should process your events. If that’s your setup and it’s going to stay that way: pick OGCS, you’ll be happy with it.
For most everyone else, Kalender Sync is the better choice:
- The sync runs 24/7 server-side — even with your computer off: phone events, vacation, weekends, no double-booking gap
- Works with every device: Mac, phone, web, “New Outlook”, M365 without desktop apps
- 9 provider types instead of 2 — including iCloud, GMX, WEB.DE, CalDAV, and iCal feeds
- Visibility levels per sync (“busy only”, “title + time”, full details) for a clean separation of work and private life
- GDPR-compliant with hosting in Germany and a DPA for business
- 2-minute setup, no installation, no updates, nothing to maintain
You can even combine them: some people run OGCS on their work PC and use Kalender Sync for everything that has to work device-independently.
Bottom line: OGCS is the best free tool in its niche — but that niche is smaller than it sounds. As soon as more than one Windows PC is involved, or the sync has to stay current when your computer isn’t on, a server-side service like Kalender Sync is hard to get around.
Try Kalender Sync for free — 1 sync free forever, setup in 2 minutes
Frequently Asked Questions
Is OGCS really free?
Yes, completely. OGCS is open source and funded by voluntary donations (donating £10 or more hides the splash screen). No features are behind a paywall.
Does OGCS work with “New Outlook”?
Only partially. The stable v2 version needs classic Outlook desktop (COM integration). For New Outlook there’s the v3 line, which works through the cloud interface — but as of July 2026 it’s alpha software. If you want a stable sync today without classic Outlook, you need a server-side service like Kalender Sync that talks directly to the official cloud APIs.
Does OGCS sync while my PC is off?
No. OGCS runs locally — no running computer, no sync. Events you create on the go only appear in the other calendar after the next start. Kalender Sync, by contrast, runs server-side around the clock.
Can OGCS transfer availability only (“free/busy”)?
OGCS can be configured at the attribute level (e.g. omit the description), but it’s designed around full event copies. Three clearly separated visibility levels per sync connection — busy only, title + time, full details — are the core concept of Kalender Sync, especially for keeping private and work calendars apart.
