I've been trying to encourage more "Charityware" for software [0]. My software is free and open source (MIT license) [1] but I also sell it for $5 and donate $3.50 of every sale to a cost-effective charity. My goal is to increase donations to the charity, and asking people for donations wouldn't be as effective. My software now has generated almost over $9,000 in donations.
Personally, every purchase of my software feels rewarding. It's probably not as great as a regular donation, but it's a close second. Furthermore, since my software is pay-what-you-want (with a minimum of $5) people have been often giving more than the minimum. That really feels like a donation.
[0] https://medium.com/@whyboris/charityware-doing-good-with-pro...