Dudle - Dudle is an online scheduling application, which is free and open source.
Delibroom - The system for meetings management that enhances office utilization. It allows to book a room with a built-in planner right in smartphones and tablets.
FullCalendar - FullCalendar is an open-source JavaScript event calendar.
BookingLive - Booking Live Online Booking System and Ecommerce Reservation Software
Framadate - Make your polls
MIDAS - MIDAS is a web based Room Booking & Resource Scheduling Software system. Available to download & run on your server or as an online hosted cloud application