I've just launched a Patreon page to allow people to financially support the development of FotoSketcher: https://www.patreon.com/FotoSketcher
Of course this is entirely optional. FotoSketcher remains 100% free, even for commercial use.
As I recently shelled out over €1000 for my development setup, I thought I might try out Patreon as a revenue source.
Some users have also made donations via PayPal (https://www.paypal.me/FotoSketcher) and I take the opportunity of this post to say a big thank you! Many a cup of coffee was bought thanks to these donations :)