I've been using a lot of different calendar systems since we've started our B&B in Utrecht (Netherlands) and never was really satisfied until this avvie calendar came along. It was easy to place the calendar on my website, which allows guests to see when we have rooms available. We have 3 rooms, and I always wanted to have a different calendar for each room (On the room detail pages on our website, so that guests with preference for a certain room can see the availability for it.) and a general calendar on my home page which combines the availability of these 3. So far everything works exactly the way I want it to. The reservation system behind it also works well, I esspecially like the fact that I have a good visual overview of all rooms and reservations, being either booked or pending (when I'm still waiting for the deposit to be paid) or a request. Also there is room for notes, arrival info, etc. I find it useful to have everything together, instead of messing around with stickies, excel sheets, and what not.
I've had an iPhone for about 6 months now and recently got the app for the avvie calendar. Although it doesn't give you all the functions the reservation system on the internet has, it does make it possible to quickly answer to reservation requests with standard emails, create new bookings, etc. I find this esspecially practical when I'm out having dinner, or on a short trip without my laptop.
Worth checking out,
Drew