Reminder Commander - Reminder manager that reminds you about important events in advance.
Qloapps - Open Source System - Build Hotel Booking Website and Manage Online & On-Desk Bookings.
Date Reminder - Date Reminder reminds you of recurring or nonrecurring events, like birthdays, bills to pay...
FewohBee - Web based management tool for hotels, pensions, accommodations and vacation homes
Scheduled tasks - GNOME GUI for configuring a users' cron (automatic jobs). Some of its features are:
BSI Hotel Booking System - BSI Hotel Booking System is a real time online hotel booking.