Just wanted to anounce our online reservation system Planyo that also comes with a Drupal plugin. I'm in the process of integrating the plugin with Drupal itself but for now you can download the module on our website.
Planyo is very flexible and allows bookings of any kind of resources (e.g. accommodation, tennis courts, yachts, appointments). Please see the booking system's homepage for more info. We also have an API for advanced usage and an affiliate program.
Best regards,
Rafael Zwiegincew
Planyo.com