Dudle - Dudle is an online scheduling application, which is free and open source.
Qloapps - Open Source System - Build Hotel Booking Website and Manage Online & On-Desk Bookings.
Pulse 24/7 - Booking & scheduling mobile app for service providers
FewohBee - Web based management tool for hotels, pensions, accommodations and vacation homes
MakePlans - Online appointment booking - MakePlans
BSI Hotel Booking System - BSI Hotel Booking System is a real time online hotel booking.