My question wasn't explanatory, sorry. I writing an app with Lazarus/FPC that requires billing customers. I've included so far in app Proposals, Sales Orders and Invoicing. But, didn't want to write the accounting, maybe not even include it but one my fellow photographers suggested it would be nice but I think he knows less about accounting than I. It's on the back burner until I change my mind.
Way back in 2006, I purchased an accounting system with source code in Delphi but it was a pain to modify vertically for the company I was contracted to write the new system.
I was just curious if anybody had worked on a project that required molding in the accounting part without developing it from scratch written in Lazarus.