the foundation gets a x amount of donation. they can spend 100% of that for anything in their bylaws. paying for devs, conferences, paying freelancers to fix bugs. They wouldn't have to pay income tax if they spent 85% of the income during the year so the incentive would be to spend almost all of the funds received.
Here are some details about the legal entity they set up for that. They are set up as a eingetragener Verein (registered voluntary association).
https://en.wikipedia.org/wiki/Registered_association_(German...