Things have come a long way since I started to develop my own hotspot backend. It now has PayPal and Subscriber support. The administration backend was written by another lad but essentially that's just a PHP interface to the database. I few extra scripts such as the PayPal IPN receiver and a subscriber account scrubber cron job runs in the background.
The interface supports Mikrotik RouterOS and the Colubris MSC series. It's not difficult to add different Access Controller types. Once again I will be looking at making the Access Controller stuff modular to make additions easier.
At some stage I will write in my own administration interface. Its a fairly large task in its own right when you consider that I have to support multiple locations with their own pricing plans with various pricing items. Throw in all the user management and invoicing/revenue sharing among locations and its a complicated task that requires a fair bit of thought.
I'm definitely getting better at coding in Perl at least. I still have a fair bit to learn about more advanced aspects of the language such as Object Oriented Programing (OOP) and package/module writing, probably best to start on the packages/modules first.