I've discovered few days ago on on Google Code an interesting XOOPS module for Hotel Room Reservation!
While it is 5 years old, it seems very advanced, and it got very good score from Scrutinizer:
But it was hard to understand sometimes the features, because it was hard-coded in Chinese. So the first thing that I did was to convert it to use language variables and upgrade it to XOOPS 2.5.x GUI, and now it should be easier to study it
At the moment I don't know if it will be generic enough to use it, but at least we should be able to extract some ideas and some code for other modules.
Anybody wants to help? You know the drill: FORK IT and contribute back!