I produced this code (PHP) 20 years ago, it served as a bookkeeping tool for my small computer business. Basically the app allowed me to:
- create sales invoices, manage client records
- create price offers, manage price lists
- book cash receipts, process incoming payments
- store purchase invoices
- store cost invoices
- calculate quarterly VAT balance
- extract yearly VAT listing
- read/send private messages from/to my assistent
This code is nothing to be proud of, I had no intent to do it according to OOP principles. It was just procedural programming.
Disclaimer: this code is old, md5 hashes are no longer secure today.