AirPrint software

I have seen a programme called Printopia where you can print from your iPhone or iPad to a non-AirPrint compatible printer IF you can print from your Mac, which is very good for a $20 outlay, only problem is your Mac needs to be ON.

Does anyone know of good software where you can print on your Wi-fi printer from your pad/phone via your router?

Thanks in advance,

Iain.