The cloud GO Contact Sync Mod alternative: ContactZapp vs GO Contact Sync Mod
GO Contact Sync Mod is a free, open-source Windows utility on SourceForge that syncs classic desktop Outlook with Google. ContactZapp is a cloud web app that keeps one clean contact list across Google, Microsoft, Apple and CardDAV — with duplicate merging and a 12-month undo history.
Free plan: 2 accounts and 100 synced contacts. No time limit.
Which tool fits your setup?
GO Contact Sync Mod has helped Windows users sync classic Outlook with Google for years, while ContactZapp is built for cloud accounts, modern Outlook apps and multi-account duplicate cleanup.
You want hands-off cloud sync, modern Outlook support and duplicate cleanup
- You have moved to the new Outlook for Windows, a Mac, Outlook on the web or mobile — where classic Outlook COM utilities cannot run.
- You want contacts to sync in the background while your PC is off, without Windows tray prompts, .NET errors or interrupted local sync passes.
- You also use Apple iCloud or CardDAV (Fastmail, Nextcloud, Purelymail) alongside Google and Microsoft.
- You want to find and merge duplicate contacts across accounts, with an automatic backup before the first change and a 12-month undo history.
You want a free open-source Windows utility for classic Outlook
- You work on a Windows PC (Windows 7 to 11 with .NET Framework 4.7.2+) and use classic desktop Outlook (Outlook 2003 to 2019 or the classic Microsoft 365 desktop app).
- You want a 100% free, open-source (GPL) desktop program with no contact cap and do not mind keeping your PC and classic Outlook running for sync.
- Your contacts live in a local Outlook PST file and you want direct PC-to-Google sync without connecting a cloud Microsoft account.
- You also want to sync classic Outlook calendar appointments to Google Calendar from your Windows desktop.
How ContactZapp and GO Contact Sync Mod compare
Every GO Contact Sync Mod detail below comes from its SourceForge project documentation (googlesyncmod), checked on 9 November 2026.
| Feature | ContactZapp | GO Contact Sync Mod |
|---|---|---|
| How it runs | Cloud web app — runs in the background with your computer off | Windows desktop utility — runs on your PC while classic Outlook is installed and accessible |
| Supported platforms | Yes: Any browser on Windows, Mac, Linux, iPhone, iPad or Android | No: Windows 7 to 11 with .NET Framework 4.7.2+ and classic desktop Outlook only |
| New Outlook for Windows & Mac | Yes: Works with New Outlook for Windows, Outlook for Mac, web and mobile via your Microsoft cloud account | No: Classic desktop Outlook (COM interface) only |
| Services connected | Yes: Google (Gmail and Workspace), Microsoft (Outlook.com, Hotmail and Microsoft 365), Apple iCloud and any CardDAV server | Classic desktop Outlook and Google Contacts only (no iCloud, no CardDAV) |
| Sync direction | Yes: Two-way or read-only per account | Yes: Two-way (Merge, Outlook Wins, Google Wins) or one-way (Outlook to Google or Google to Outlook) |
| Sync schedule | Hourly, daily or manual (starts on manual so you stay in control) | User-defined timer on the PC or manual sync |
| Contact fields synced | Yes: Names, emails, phones, addresses, company, job title, notes, birthdays, photos, websites, related people, IM, custom fields and labels | Yes: Standard Outlook fields, photos, notes, categories/groups and multiple phone/email fields |
| Custom fields across services | Yes: Carries custom fields (label and value) across Google, Microsoft, iCloud and CardDAV | No: Does not sync custom fields to Apple iCloud or CardDAV |
| Duplicate finding and merging | Yes: Finds duplicates within and across accounts by name, email, phone and address; side-by-side manual merge or optional Auto-Merge | No: Matches contacts during sync, but has no standalone cross-account duplicate scanner or side-by-side merge review |
| Merge field preservation | Yes: Keeps every phone number, email and address when merging two contacts, and prefers the fuller version of names, phones and addresses | Conflict prompt asks which side wins (Merge Prompt, Outlook Wins or Google Wins) |
| Pre-sync backup | Yes: Automatic backup before the first change, plus up to 5 saved vCard backups per account | No: No built-in vCard backup archive before writing changes |
| Undo and change history | Yes: Every change is kept for 12 months; roll back 1 contact, 1 sync run or everything | No: No undo history or point-in-time rollback |
| Calendar and notes sync | No: Contacts only — built to do one job well | Yes: Syncs classic Outlook Calendar appointments (and legacy notes) with Google |
| Price | Free plan (2 accounts, 100 contacts synced, no time limit). Paid plans from $9.99 / €8.99 a month | Free and open-source (GPL); accepts optional donations |
Swipe the table to see every column
Keep syncing when you leave classic Windows Outlook behind
GO Contact Sync Mod is a community-maintained Windows desktop tool that talks directly to classic Outlook through Microsoft's desktop COM interface. That architecture means it only works on a Windows PC with classic Outlook and .NET Framework 4.7.2+ installed. If you switch to the new Outlook for Windows, move to a Mac or manage contacts from your phone, GO Contact Sync Mod cannot connect.
ContactZapp runs in the cloud. You connect your Google and Microsoft accounts once in the browser using OAuth, and ContactZapp syncs your contacts directly between the providers' cloud servers — plus Apple iCloud and CardDAV if you use them.
- Works with every Outlook app: Because changes are written directly to your Microsoft 365 or Outlook.com account, updated contacts appear in New Outlook for Windows, Outlook for Mac, classic Outlook, web and mobile.
- Adds Apple iCloud and CardDAV: Bring iCloud, Fastmail, Nextcloud, Purelymail or any other CardDAV address book into the same sync loop.
- No PC background tray app: Your contacts stay in sync while your computer is asleep or turned off.
Fix duplicate contacts instead of clicking through conflict pop-ups
Anyone who has synced Outlook and Google over the years knows how easily duplicates pile up — especially when a desktop sync pass is interrupted, an Outlook profile is recreated or the same person is saved under slightly different names in two accounts.
GO Contact Sync Mod asks which side should win during a sync conflict (Outlook Wins, Google Wins or Merge Prompt), but it is not designed to scan and clean up existing duplicates across accounts. ContactZapp is built specifically to find and merge duplicates without losing data.
- Finds duplicates within and across accounts: Matches contacts by name, email, phone and address across Google, Microsoft, Apple and CardDAV.
- Never drops a second phone or email: When you merge two contacts, ContactZapp keeps every phone number, email and address. For single values like company, job title or photo, the newest value wins — or you can set a primary account.
- Prefers the fuller version: When two accounts write the same detail differently, ContactZapp keeps "John Doe Jr" over "J. Doe", a number with its country code over one without and an address with the postcode over one without.
An automatic backup before the first change, plus 12 months of undo
When a local desktop sync goes wrong — for example, if the wrong sync direction or deletion rule is selected — there is no built-in "undo sync run" button in GO Contact Sync Mod. Cleaning up hundreds of overwritten or duplicated contacts by hand takes hours.
ContactZapp is designed so every sync and every merge is reversible. New users start on manual sync with Auto-Merge turned off, so nothing changes until you tell it to.
- Automatic pre-write backup: ContactZapp takes a full backup of each account before making the first change, and lets you keep up to 5 downloadable vCard backups per account.
- 12-month change history: Every edit, merge and deletion is kept for 12 months. Roll back 1 contact, 1 sync run or everything, and ContactZapp sends the rollback to your accounts.
- Read-only accounts: Set any account to read-only if you want to pull its contacts in without ever writing changes back to it.
Move from GO Contact Sync Mod to ContactZapp in 3 steps
You can transition from local desktop sync to cloud sync in a few minutes without losing any of your existing Outlook or Google contacts.
- STEP 01
Turn off Auto Sync in GO Contact Sync Mod
Open GO Contact Sync Mod from your Windows system tray, uncheck Auto Sync (or exit the app) so it stops running local sync passes in the background.
- STEP 02
Connect your accounts in ContactZapp
Sign in to ContactZapp in your browser and connect your Google and Microsoft accounts — plus Apple iCloud or CardDAV if you use them. ContactZapp backs up each account before making the first change.
- STEP 03
Clean up duplicates and set your schedule
Review the duplicates found across your accounts and merge them side by side (or enable Auto-Merge). Then switch ContactZapp from manual sync to daily or hourly.
Questions about GO Contact Sync Mod and ContactZapp
Why does GO Contact Sync Mod not work with the new Outlook for Windows?
GO Contact Sync Mod connects to Outlook on your PC through the classic desktop COM interface. Microsoft's new Outlook for Windows is built on a web architecture that does not support classic COM utilities. ContactZapp syncs directly with your Microsoft account in the cloud, so it works with New Outlook for Windows, classic Outlook, Outlook for Mac, Outlook on the web and mobile.
Can I use ContactZapp on a Mac, iPhone or Android without a Windows PC?
Yes. ContactZapp is a cloud web app that runs in any browser and syncs directly between Google, Microsoft, Apple iCloud and CardDAV servers. Your iPhone, Android phone and Mac receive the updated contacts automatically through the accounts they already sync with.
How does ContactZapp handle duplicate contacts created by earlier sync tools?
When you connect your accounts, ContactZapp scans within each account and across accounts for duplicate contacts by name, email, phone and address. You can review and merge them side by side — keeping every phone number, email and address — or turn on Auto-Merge. Every merge can be undone for 12 months.
What if my classic Outlook contacts are in a local PST file?
If your contacts are saved in a local-only PST file that is not linked to a Microsoft 365 or Outlook.com mailbox, move or copy those contacts once into your Microsoft cloud Contacts folder in classic Outlook. Once they are in your Microsoft account, ContactZapp keeps them synced in the cloud.
Does ContactZapp sync Outlook Calendar appointments like GO Contact Sync Mod?
No. ContactZapp is built specifically for contacts — syncing across Google, Microsoft, Apple and CardDAV, merging duplicates and keeping a 12-month undo history. It does not sync calendar events.
GO Contact Sync Mod is free — does ContactZapp have a free plan?
Yes. GO Contact Sync Mod is free and open-source (GPL) for Windows desktop users. ContactZapp offers a free plan with no time limit and no credit card that connects 2 accounts and syncs 100 contacts between them (working with an address book of any size). If you need more than 100 contacts synced or 3+ accounts, paid plans start at $9.99 / €8.99 a month with a 14-day money-back guarantee on your first purchase.
Ready to sync Outlook and Google contacts in the cloud?
Connect 2 accounts on the free plan. Sync 100 contacts, merge duplicates and keep a 12-month undo history — no credit card and no time limit.