Two are quickbooks and freshbooks. You really should study accounting if you've never seen discounts tied to the date paid. Cash flow is important to every business, and a lot of businesses do give discounts for quick payment.

http://www.freshbooks.com/blog/the-best-invoice-payment-term...

https://www.americanexpress.com/us/small-business/openforum/...

Being able to define your payment terms is important.