Amai PreOrder Manager + Notify

I really love the automatic enabling of the pre-order status once an item's stock drops to zero. The dashboard is really well layed out and the documentation was clearly written. I did have some problems implementing the code due to conflicts with my store's theme. I emailed Philip and he promptly responded with suggestions how to fix the issues I had after looking at my theme code. I applied the fixes and voila! I was up and running. I did not expect this level of service from a free app. So far I'm really pleased with the whole experience.
UPDATE: I switched to a new theme recently and I was having trouble getting the app to update properly. These guys took care of it within an hour after after sent the email. Still impressed.