Tool comparison
Kalender Sync vs. Cal.com – open-source booking plus German sync
Same story here: not either-or. Cal.com is a booking tool – and a really good one, open source and self-hostable if you want. Kalender Sync is a sync tool. The pain Cal.com alone doesn't solve: it checks availability only in the calendars you've connected. Events in calendars you can't or won't connect stay invisible – and get double-booked. That's exactly what Kalender Sync is for.
Background
What can Cal.com do?
Cal.com is the open-source alternative to Calendly: booking pages, event types, team features and an open API – as a hosted service or fully self-hosted (the source code lives on GitHub, with deployment via Docker among others). The free plan for individuals is permanently free and allows unlimited calendar connections; teams pay $12, organisations $28 per user/month (billed annually). The key point for this comparison: Cal.com, too, only checks for conflicts in the calendars that are actually connected – whatever's missing counts as free and gets offered for booking.
Strengths
Where Cal.com is strong
Open source and self-hostable
The entire codebase is open; if you want full data control, you run Cal.com on your own infrastructure. For self-hosters, privacy purists and developers, that's a genuine differentiator among booking tools – and an approach we openly respect.
Generous free plan
Unlike the market leader, the free individual plan includes unlimited calendar connections. If you can connect all your calendars, the availability check is already well covered.
A platform, not just a tool
API, webhooks, apps, white-label: Cal.com is built as scheduling infrastructure. If you want to embed booking into your own product, this is the most flexible foundation.
Fair team pricing
$12 per user/month for teams undercuts comparable booking tools – with open code and no vendor lock-in.
Where Kalender Sync wins
What Cal.com doesn't solve – and Kalender Sync does
Being able to connect isn't the same as having connected
Unlimited calendar connections only help with calendars you're actually allowed to connect. Your client's M365 tenant where third-party apps are locked down, the family's GMX calendar, the second engagement: in practice, gaps remain – and your Cal.com page offers slots you've long since filled. Kalender Sync mirrors all of it as "Busy" into exactly the calendar Cal.com checks.
German providers connected directly
Kalender Sync connects 9 provider types – including GMX and WEB.DE, the big German consumer providers that regularly fall through the cracks in booking setups. Their events reliably end up where your booking tool looks.
Three visibility levels per sync
You choose per synchronisation what arrives: "Busy" only, "Title + time" or full details – with a custom display name for blocked slots. Your work calendar gets blocked without private details travelling along. Data minimisation is the default, not the limit.
Two-way sync and live-sharing
Kalender Sync synchronises bidirectionally and can embed your availability into another person's calendar by invitation – as real events, not an ICS subscription. For colleagues, assistants and long-term clients, that's a better channel than a booking link.
GDPR without running your own server
Full data control with Cal.com comes via self-hosting – meaning a server, updates and operational responsibility. Kalender Sync delivers German data protection ready-made: GDPR- and BDSG-compliant, hosted at Hetzner in Nuremberg, DPA for business customers included – run by a German company.
An affordable add-on layer
One synchronisation is permanently free, Basic costs €4/month (5 accounts), Business €10/month (unlimited) – with a 14-day Business trial, no credit card. The sync layer under your booking setup costs less than a single team seat.
Decision guide
When should you pick which?
You use Cal.com (and keep it) if:
- You need booking links – meetings should be bookable from the outside.
- Open source, self-hosting or an open API matter to you.
- You want to embed scheduling into your own product or stack.
Kalender Sync joins the stack if:
- Your booking page offers slots you've long since filled – because not all calendars are connected or allowed to be.
- You need calendars from external tenants or providers missing from the booking tool: 9 provider types – Google, Microsoft Outlook/M365, Apple iCloud, GMX, WEB.DE, mailbox.org, Infomaniak kSuite, CalDAV and iCal feeds. Kalender Sync is the only tool in this comparison that connects the German providers GMX & WEB.DE.
- Private events should only appear as "Busy" – you choose the detail level per sync.
- You additionally want to share availability live with specific people – via two-way sync and live-sharing instead of a booking link.
- You want German data protection with a DPA, without running a server yourself.
Keep Cal.com – give it the full scheduling truth
Kalender Sync mirrors every one of your calendars as "Busy" to where your booking tool checks. GDPR-compliant, hosted in Germany, from €0.
Try free for 14 daysCurrently supported providers
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