Open Source Booking System
A booking system is really a concurrency problem wearing a calendar. Its core job is preventing two people from grabbing the same slot while still showing accurate availability across staff, rooms, or equipment, and everything else - reminders, payments, nice themes - sits on top of that. Hosted schedulers solve it, but they also hold your appointment history and your customers' contact details, and often meter bookings or seats. The open source options here run the scheduling engine on your own server, syncing with external calendars and handling time zones, buffers, and cancellation rules, so the reservation data and customer information stay with you rather than a scheduling vendor you rent by the seat.
Cal.diy
Self-hosted scheduling platform for individuals and self-hosters, the community edition of Cal.com
QloApps
Open-source hotel reservation system with a PMS, booking engine, and hotel website
Rallly
Open-source meeting poll tool for finding a date and time that works for the whole group
Easy!Appointments
Self-hosted appointment scheduler with customer management and Google Calendar sync
TastyIgniter
Open-source online ordering and table reservation system for restaurants and takeaways
LibreBooking
Open-source resource scheduling for reservations, waitlists, quotas, and usage reporting
classroombookings
Open-source room booking system for schools with self-hosted and hosted options
GYM One
Open source web software for managing gym members, classes, tickets, payments, and access control
Our picks
Best for service appointments: Easy!Appointments Easy!Appointments is a self-hosted scheduler for appointment and customer management, organized around services, providers, and working plans with booking rules. It syncs with Google Calendar, sends email notifications, and offers a multi-language interface, and it is free for personal and commercial use. A solid general-purpose choice for businesses booking staff time against services.
Best for shared rooms and equipment: LibreBooking LibreBooking is resource-scheduling software for organizations reserving shared spaces or gear. It supports multi-resource booking, waitlists, quotas, and credits, with role-based access control and usage reporting, and integrates with Outlook and Thunderbird through ICS. A fork of Booked Scheduler, it self-hosts on PHP and MySQL or as a Docker container - the pick when bookings consume limited resources, not just calendar time.
Best for hotels: QloApps QloApps is a hotel reservation system that combines a property-management system, a booking engine, and a hotel website in one install. It manages on-desk and online reservations with multilingual and multicurrency support, and runs on a PHP and MySQL stack or a Docker image. The right fit when your inventory is rooms and nights rather than appointment slots.
Best for group availability polls: Rallly Rallly solves a narrower problem: finding a date and time that works for a whole group. You create a poll in seconds and share it, and participants mark availability without logging in, cutting the back-and-forth email. It self-hosts on a Next.js and PostgreSQL stack. Reach for it to agree on a meeting time, not to sell fixed booking slots.
Fitting the scheduling model to how you actually book
Everything hinges on the inventory model, because it decides whether the software fits your operation at all. A single-provider appointment calendar is a different problem from reserving seats in a class, assigning shared equipment, rotating staff, or blocking cleanup time between rentals. Easy!Appointments and Cal.diy center on provider-and-service appointment scheduling, while LibreBooking models multi-resource booking with waitlists, quotas, and credits, and QloApps handles room inventory for hotels. Check how capacity, buffers, recurring availability, and exceptions are represented before assuming a tool covers your case.
Payments and cancellation policy are the next hard boundary, because most booking failures happen after the slot is chosen. Deposits, refunds, no-show fees, coupons, taxes, and partial payments all need clear handling, and the real question is whether payment status can hold or release a reservation without corrupting your accounting records. Vertical tools carry this further into their domain: GYM One ties memberships, tickets, and payments to attendance, and TastyIgniter links table reservations to online ordering. A good fit matches your operating policy instead of forcing every exception into a notes field.
Treat calendar sync, notifications, and exports as operational infrastructure rather than extras. Two-way sync with Google Calendar or an ICS feed can create conflicts when an external edit is not mapped back to the booking record, so test recurring events, time zones, and cancellations before you rely on it. Email and SMS reminders need templates and an audit trail for when customers claim they were never notified. Before committing, run one full lifecycle - public form, admin change, cancellation, and export - and confirm customers, bookings, payments, and timestamps all come back out in a usable format.
Related categories
Frequently asked questions
How do these systems actually prevent double bookings?+
They combine availability rules with database-level locking or transaction checks when a reservation is created, so two overlapping requests cannot both win. The detail that matters is behavior under load, when two customers submit the same slot within a second of each other. Test that directly, along with admin edits, external calendar sync, and payment delays. A slot should not read as confirmed until the system has a single, consistent state.
Which tool fits my type of business?+
Match the tool to your inventory, not its popularity. Cal.diy and Easy!Appointments suit provider-based appointments; LibreBooking fits shared rooms and equipment with waitlists and quotas; classroombookings targets school rooms and timetables; QloApps is a hotel reservation system with a property-management back end; GYM One runs fitness memberships and classes; and TastyIgniter pairs restaurant table reservations with online ordering. Rallly is different again - it is a group availability poll, not a slot-booking engine.
How reliable is two-way calendar sync?+
Useful, but not the same as a booking engine, and two-way sync is where problems appear. One-way export is simpler and safer; two-way sync introduces conflicts when an external event is moved, deleted, or edited without booking metadata. Cal.diy integrates Google Calendar and Office 365, and Easy!Appointments and LibreBooking sync through Google Calendar or ICS. Test recurring events, time zones, and admin overrides before trusting sync for availability decisions.
What payment features should a booking tool handle?+
Look past basic card acceptance to deposits, full prepayment, pay-later bookings, refunds, cancellation fees, invoices, taxes, and coupons - and how payment status ties to reservation status. The revealing case is a failed payment: does the slot stay held, expire automatically, or need manual cleanup? Vertical tools like GYM One and QloApps carry payment tracking into memberships and hotel stays, where booking and accounting records most easily drift apart.
What time zone and daylight saving edge cases should I test?+
Test bookings around daylight saving transitions, customers in other time zones, remote staff, and resources tied to a physical location. The system should store times consistently and display them clearly to both sides, and confirmation emails, calendar invites, and reminders should all show the same local time. Watch for duplicated or missing hours during clock changes, which quietly produce wrong appointment times and no-shows.
Is Rallly a booking system in the same sense as the others?+
Not quite, and it helps to know the difference. Rallly is a group scheduling poll: you propose dates and times, participants mark availability without logging in, and you pick the slot that works for the most people. It does not manage resources, payments, or real-time availability. Use it to agree on a meeting time with a group; use the others when you are selling or reserving fixed slots.
What booking data should I be able to export?+
At minimum, customers, bookings, resources, staff assignments, payment references, cancellation records, form responses, notes, and timestamps - in a plain format you can load into a spreadsheet or database. Calendar-only exports lose the policy and transaction context that make records useful. Confirm exports preserve IDs, since those are what let you reconcile a booking against its payment, its confirmation email, and later reports.