In this thread there is a comment which says that side consulting jobs are restricted in German academia. Specifically this comment:
You can have consulting contracts in industry. You will usually need to clear this with your university, and your outside commitments will likely be capped at 8 hours per week or similar, but this can of course still mean serious money.
Would a professor at a design Hochscule be restricted in say, selling a drawing software app, photoshop plus ins, or art prints? Would permission need to be obtained? Does it need to be mentioned to the school?
Are there federal and/or state rules regarding side income, or is it determined by the institute? If it's per institute, are there any websites which aggregate this information, or is the only source of information asking the school directly?
The specific school I am thinking of seems to have a lot of faculty running their own design agencies. Are the rules different for faculty in design oriented fields vs. a field like chemistry or politics?