This post is part of my 30 days of geek challenge.

This is actually a tricky question, after all, how do you define what your greatest application is? Is greatest the largest, the most complex, the niftiest or the one that you find most useful?

I’m going to go with the Amberdms Billing System for my entry, it’s a 49,447 line PHP web application providing accounting, billing, time keeping and invoicing functionality.

• Standard double-entry accounting.
• Timesheets/timekeeping.
• PDF invoice generation
• ISP service billing, including data usage and VoIP call record charging.
• Mostly object orientated PHP built on the Amberphplib framework.
• Fully open source under the GNU AGPL software license.

It’s fully open source and my startup Amberdms Ltd provides hosted versions as well as software development/customisation services around it.

Reason for the selection is that it’s the largest/most complex application I’ve written, as well as having some significant uptake by others.

It also lead to the development of the Amberphplib framework, which whilst not perfect, has become a valuable base for a number of my web applications and provided a huge learning curve for building the next generation web application frameworks in future.