I am looking for a calendar which will act as a 'bookings' calendar for holiday apartments and also link in with all the other information I hold in filemaker database (inventories etc). Will any of your calendars fit the bill for this? I would want to view the apartment bookings seperately and also all together so the vacancies would show easily.

Sure. SeedCode Calendar will treat your apartments as resources and link appointments (rentals) to a resource. You can then assign types to these rentals (pending, confirmed, etc.) to keep things straight and even use other "types" for things like meetings or deadlines so you can filter the calendar to just show these other types of appointments apart from your bookings.

Download the 10-day demo of SeedCode Calendar, enter your apartments as Resources and then enter some bookings to see how it works.