I was wondering if it is legal to offer a free software with limitations, then offer to give different license keys for donations.
In this case, it is a software for file uploads to different one-click-hosters. As free user, you can upload XX GB, then your speed and number of simultaneous uploads will be limited. If you donate more than 3$, you get a license key and become a registered user. Then you can upload 50GB a day (on average, you can exceed it, if you don't do it often). If you exceed this limit too much/often your license key will be disabled and you will be asked (via email) to "donate" 5$ a month to increase your traffic by 200GB a day.
Is this legal? Can you accept donations as a form of payment? Donations are done via paypal.