Cal.com Goes Closed Source: Best Open Source Alternatives in 2026

On April 15, 2026, Cal.com moved its production codebase behind closed doors. The public calcom/cal.com repository was renamed calcom/cal.diy — a separate, community-driven fork that no longer mirrors what runs in production. The official reason: AI-powered vulnerability scanners (Anthropic's Mythos research, plus tools used by attackers in the wild) are now finding bugs in hardened code faster than maintainers can patch them. Whatever you think of that reasoning, the practical effect is the same: the most popular open source Calendly alternative is no longer open source. If you self-hosted Cal.com because it was open, or you were about to, this is the moment to look around.

The short version: Cal.diy is the closest continuation if you want to stay on the same codebase, but it's a fork, not the production app. Easy!Appointments is the most mature self-hosted booking tool that's still fully open. Rallly solves group scheduling, not 1:1 booking. SavvyCal, Calendly, and Zoho Bookings are commercial choices if you're done self-hosting. And if your real problem is what to do with the time after the meeting is booked — building deep work blocks, defending focus time — a dedicated AI calendar like Reclaim, Motion, or Temporal is a different category that solves a different problem. This guide walks through all of them honestly.

What actually changed at Cal.com

Cal.com's CEO Peer Richelsen announced the change on the company blog, citing a security firm's claim that open-source applications are now 5–10× easier to exploit than closed-source ones. The company points to two recent incidents: a critical authentication flaw (CVE-2026-23478) and a broken access control bug found by Gecko Security that exposed bookings and enabled account takeover.

The new structure has two pieces:

• Cal.com (production) — closed source, hosted at cal.com, used by paying customers and the free hosted plan.
• Cal.diy — the renamed public repo, MIT-licensed, community-maintained. Cal.com says it will accept contributions but won't sync production code into it.

Reaction on Hacker News and Slashdot has been mixed. Some developers accepted the security argument. Many called it a business move dressed up as security — pointing out that "AI can read your code" is true for any codebase, and that the real motivation is to protect commercial differentiation as Cal.com pushes upmarket. Either way, the codebase divergence is real. If you self-host today, you'll keep getting community patches on Cal.diy, but the production-grade features (newer integrations, billing, enterprise SSO) are now behind closed doors.

Cal.diy

The pitch. Same code you knew, new name, fully open source going forward — with a community team rather than a venture-backed one.

What it does well

• Drop-in continuation. If you've already self-hosted Cal.com, switching to Cal.diy is cosmetic for now. Same Next.js stack, same Postgres schema, same Docker setup.
• MIT license. No rug pull at the license layer. Forks are permitted.
• Active community. Within a week of the announcement, several maintainers started organizing a release cadence and triage rotation.

What it doesn't do well

• It's a fork without the upstream. Production Cal.com will diverge from day one. Bug fixes won't necessarily flow back. New integrations launched on Cal.com (Salesforce, HubSpot deep links, etc.) may never land here.
• Governance is unproven. A community fork lives or dies by who shows up. The first six months will tell.
• Enterprise-grade features will lag. SSO, audit logs, and compliance certifications take a paid team. Don't expect SOC 2 from a volunteer fork.

Who it's actually for. Self-hosters who already run Cal.com and want continuity. Indie hackers who want to keep tinkering with booking page code. Anyone willing to trade "always current with the SaaS" for "controls everything I run."

Easy!Appointments

The pitch. A no-frills, completely open-source appointment booking system that's been around since 2013. Boring, in the best sense.

What it does well

• Truly free, truly self-hosted. PHP/MySQL stack — runs on shared hosting if you want it to. No cloud dependencies, no telemetry.
• Service-business shaped. Multi-staff scheduling, service categories, business hours, client records. Designed for clinics, salons, consultants — where Cal.com leans more SaaS-team-oriented.
• Google Calendar sync. Two-way sync is supported and stable.

What it doesn't do well

• Looks dated. UI is functional but not modern. If your booking page is a brand surface, this isn't the one.
• No native AI features. No smart routing, no round-robin with load balancing, no AI-suggested times.
• No team features in the SaaS sense. Round-robin works for staff, but it's not built for sales teams running pooled lead routing.

Who it's actually for. Solo service providers and small clinics who want a free, durable booking tool they can run forever without a subscription. Not the right fit if your use case is "PM scheduling 1:1s with engineers."

Rallly

The pitch. Open-source group scheduling — the Doodle replacement, not the Calendly replacement.

What it does well

• Zero-friction group polls. Send a link, attendees vote on times, you pick the winner. Works without accounts.
• Self-hostable. Docker image, Postgres, ten minutes to a working instance.
• Clean UI. Easily the best-looking tool on this list.

What it doesn't do well

• It's not a booking tool. "Find a time everyone can do" is a different problem than "let prospects book a slot on my calendar." If you need the second, Rallly will frustrate you.
• No payment integration. No Stripe, no paid bookings.
• Limited integrations. Calendar sync exists but is thinner than Cal.diy or Easy!Appointments.

Who it's actually for. Teams coordinating internal meetings, group dinners, project kickoffs. Replace Doodle with this and never look back. Don't try to make it a Calendly.

SavvyCal (commercial, but worth mentioning)

The pitch. The polished commercial 1:1 booking tool that beat Calendly on UX and overlay scheduling.

What it does well

• Overlay scheduling. The killer feature: send a recipient a link, they overlay their own calendar onto yours, and pick a time that's mutually free. Reduces the "back-and-forth on three options" loop that plain Calendly creates.
• Round-robin and meeting polls. Both modes exist and work.
• Reasonable pricing. $12/month per user for the Basic plan, $20/month per user for Premium (SavvyCal pricing).

What it doesn't do well

• Not self-hostable. Closed source, US-hosted SaaS only.
• No AI scheduling. It's a booking tool, not a planner. It won't move your tasks around or protect your focus time.

Who it's actually for. Someone moving off Cal.com who's done with self-hosting and wants the most thoughtful 1:1 booking UX on the market. Not for PMs trying to plan deep work.

Calendly

The pitch. The default. The one your prospects already know how to use.

What it does well

• Ubiquity. Recipients don't need an explanation. The booking flow is muscle memory by now.
• Deep integrations. Salesforce, HubSpot, Stripe, Zoom, Microsoft Teams, Google Meet — all polished.
• Routing forms and team scheduling. Sales teams using Calendly for inbound lead routing get real value here.

What it doesn't do well

• Pricing creeps fast. Free tier is restrictive. Standard at $12/month per user, Teams at $20, and the routing forms that sales teams need sit on Teams or higher (Calendly pricing).
• Closed and proprietary. If "open source" was your reason for picking Cal.com, Calendly was never your tool — and switching to it is a philosophical loss.

Who it's actually for. Anyone who needs a booking tool to just work with the lowest possible recipient friction. The "boring, expensive, ubiquitous" choice.

When the real problem isn't booking — it's planning

A surprising number of people self-hosted Cal.com because they wanted "AI calendar" but read the marketing as "Cal.com is open and AI-ish, good enough." Those are two different categories:

Booking tools (Cal.com, Calendly, SavvyCal, Easy!Appointments) handle one job: let someone else pick a time on your calendar. They stop there.

AI calendars (Reclaim, Motion, Sunsama, Morgen, Temporal) handle a different job: turn your tasks, habits, and meetings into a planned day, and reshape it when reality shifts.

If your reason for using Cal.com was "it's the only tool I trust," fine — Cal.diy or Easy!Appointments fits. If your real frustration was "my calendar is full of bookings and I have no time to do actual work," none of the booking tools will fix that. You need a planner sitting on top of your calendar.

This is where energy-aware scheduling matters. Temporal is an AI calendar and task management app that schedules around your focus patterns and energy levels — not just time availability. It uses three AI scheduling modes (Suggest, Auto, Off), a natural-language input for tasks, and a command palette so you can rearrange your day without touching the mouse. It's not a Cal.com replacement — it doesn't generate booking links — but it solves the layer above: what to actually do in the time that's left after meetings are booked. Compared with Reclaim's auto-defragmentation or Motion's auto-scheduling, Temporal's differentiator is honest about chronotype: it asks when your brain peaks and protects that window.

If you want a deeper comparison of the AI calendar layer specifically, see our breakdowns of Motion vs Reclaim vs Clockwise vs Akiflow vs Sunsama and the best time blocking apps in 2026.

Comparison table

Which tool should you choose?

You self-host Cal.com today and want minimum disruption. Switch to Cal.diy. Mirror the new repo, accept the divergence from production Cal.com, and budget time for community-paced patches.

You run a small service business (clinic, salon, consultancy) and need durable, free booking. Easy!Appointments. It's not pretty, but it will outlive every SaaS on this list.

You coordinate group meetings, not 1:1 bookings. Rallly. Anything else is overkill.

You want polished 1:1 booking and you're done self-hosting. SavvyCal for the overlay UX, Calendly for the ubiquity. Both are commercial; pick on UX preference and integration needs.

Your real problem is planning, not booking. A booking tool won't solve "I have no time for deep work." Pair your booking tool with an AI calendar — Reclaim if you want focus time defense in Google Calendar, Motion for deadline-driven auto-scheduling, Temporal for energy-aware planning around your chronotype.

A note for product managers and developers reading this: the booking-vs-planning distinction is the one most people get wrong. If you find yourself comparing Cal.com to Motion, you're comparing tools that don't solve the same problem. We covered this directly in the best calendar app for product managers and for developers.

Frequently asked questions

Is Cal.com still free to use? Yes — Cal.com still offers a free hosted plan and paid tiers at cal.com. The change is to source code availability, not pricing. If you don't self-host, your day-to-day experience is unchanged.

Can I keep self-hosting Cal.com from before April 15, 2026? You can keep running the version you've already deployed. But you won't get production updates — you'd be tracking the public Cal.diy fork, which will diverge from cal.com production over time.

What's the difference between Cal.com and Cal.diy now? Cal.com is the closed-source SaaS. Cal.diy is the renamed public fork — MIT-licensed, community-maintained, no longer mirroring production. Think of Cal.diy as the new "self-hosted edition" without the company behind it.

Why did Cal.com say AI is the reason? The argument is that AI-powered vulnerability scanners can now read open codebases faster than maintainers can patch. Anthropic's Mythos research showed AI finding flaws in hardened systems like OpenBSD. Critics on Hacker News pointed out that closed source isn't immune to AI scanning either — it just slows discovery slightly.

Are Cal.com bookings affected? No. Existing bookings, integrations, and customer data are untouched. The only change is who can read the production source code.

Is there a free open-source alternative that supports payments? Cal.diy still supports Stripe. Easy!Appointments has plugins for payment integration. Rallly does not have native payments.

Does Temporal have booking links like Calendly or Cal.com? No — Temporal focuses on the planning layer (tasks, focus blocks, AI scheduling, calendar sync). For booking links, pair Temporal with Cal.diy, SavvyCal, or Calendly. Temporal's role is what happens between the meetings, not the meetings themselves.

What should sales teams do now? If you're a sales team using Cal.com self-hosted for round-robin lead routing, the honest answer is most teams should move to Calendly or Chili Piper. Cal.diy will work, but enterprise routing features won't keep pace with paid SaaS.

Temporal is an AI calendar and task management app that schedules your day around your focus patterns and energy levels — not just time availability. It combines tasks, calendar, time tracking, and AI scheduling in one app with three automation modes: Suggest, Auto, and Off.