This original question was asked on superuser: Developing online invoicing and inventory application.
It then got migrated to serverfault, primarily because the asker talked about "his clients" meaning this was an enterprise class solution.
Now it says it has been migrated to superuser, with a link to the original question on superuser, but the text says "This question is software development or programming related, and is a better fit for Stack Overflow." and can be found on stackoverflow.
I have attached a picture with hand drawn circles for your consideration.