Hello. I just made exactly this kind of website, but according to Romanian billing requirments/format. So I think I can adapt that. The website can do the following: Register your company data(name, adress, government-given identification number etc), register your clients data, register invoice serials(this is tied to Romanian legislation, where every invoice needs to have a serial and a number), and finally create the invoice(you can enter buyer, seller(aka you) data, price, VAT, invoiceing date(the date when you legally create the invoice, a bit hard to translate), invoice period, and a text zone where you write what kind of service are you invoiceing). I know this sound a bit wierd, but I can not translate it better because this are economical/lawyer terms, and I am a programmer, not lingvist. The webpage also creats the invoice in pdf format and keeps track of payed/unpayed status and totals