alt Hacker NewsIn addition to tax stuff there's a card you can get in most states, issued by cities/districts based on certain criteria, like doing a certain amount of hours per week of volunteer work, that will give you a discount or free entry to museums, pools, movie theaters, events.. There's listings online of all the institutions and businesses that give a discount.
For this, and for the criminal justice use case, it seems to me that it isn't possible for "work on open source" to receive this kind of formal recognition. Anyone is free to self-certify that they're working on an open-source project headed by, and exclusively contributed to by, themselves.
You'd need to formally recognize open-source projects that the German state approves of, on a case-by-case basis.
And even then you have questions like "If Hans Reiser is sentenced to community service for killing his wife, can he satisfy that by working on reiserfs? How is that different from sentencing him to no punishment?"