bambooinvoices . org
(I AM NOT AFFILIATED WITH THEM!!!)
I would like that modified to allow multiple users to control different sets of invoices. For example, an electrician can have an account for themselves, and a plumber for himself. This way, multiple people can use the invoice software with NO overlap (keep everyones data private to their login).
This should be VERY easy to someone experienced with MySQL and PHP. Most everything is already written for you.
(There will have to be a registration page for new users to sign up, and a login page for existing users to login)