[Osiris]

It's a one-time sale. It's a freemium model. You can download the app and get limited functionality. You can purchase for $10 the "Pro" version which is a serial number that unlocks the advanced features.

For a while I was doing cheaper time-limited licenses, like $1 for 6 months, $2 for 1 year, etc and $10 for lifetime.

Best source of customers is from free users. I started the app as free until version 3.0 when I switched to freemium. Sales have been fairly consistent each month for years, with spikes when a blog picks it up.