I want to run a business. I issue an asset (let's call it Krusty Krab tokens - KKT). I set quantity of KKT to 1000. I announce that I sell KKT for 20 NXT each and pay 5 NXT monthly interest within next 6 months. I create an ask order -- 1000 KKT for 20,000 NXT.
You create a transaction that sends me 500 NXT for 25 KKT. It's up to you what to do with your 25 KKT (you can place an ask order and sell them for 27 NXT) but each month I will check the blockchain to see who owns KKT. And I will send 5 NXT for each KKT to those who owns them.