"Freelance software development", problem solved. Not that the tax authority cares at all where the money comes from. They don't have a "cash income" category because they have a deep and burning desire to know these things. They're primarily busy with taking their cut.

It might depend, on country, but I know that usually you can mention donations as "donations" in your income papers/form.

Don't know how it would be for an opensource project. Mentioning something like "open source browser extension uBlock Origin" probably...

Interesting how people report their donations, patreons, etc.

Patreon sends a 1099-K if you get more than $20K in a year.

https://support.patreon.com/hc/en-us/articles/207099566-Will...