Support "Pay what you want"

There's currently two options for payment for applications:
- Free
- A fixed price

An new method of sales is "pay what you want" which has seen great success (e.g. https://www.humblebundle.com/).

For many projects I work on it's desirable for them to be able to be installed for free as this allows the maximum number of people to take advantage of the software. These projects tend to be open source so you don't want someone to just copy the source and upload it as a free app which could happen if you had a fixed price. Donations have a reputation for not working (only a tiny percentage will give even if they manage to get through the payment process).