Horse and buggy software

I noticed two different threads on software on here right now. But niether addresses what I'm looking for right now. What do you guys use that enables a repairman to do on-the-spot billing? I have been using an ancient countertop-style register box thing. The kind that you fill out the invoice in duplicate, pull the handle and both copies pop out the end. It's getting impossible to find refills anymore.>>>

quickbooks pro microsoft works has an invoice and a purchase order wizard...but quickbooks will let you draw up an agreement, that once you print it, gets saved, and when it's time to hand over the invoice, it gives you another form. It can get really complicated, if you want it to, which is good because, you don't want to have to change systems every time your business grows to another level.... >>>