Gifts do not confer obligation. If you give me a screwdriver and I use it to run my electrical installation service business, I don’t owe you a payment.
This idea that one must “give back” after receiving a gift freely given is simply silly.
If your neighbor kept baking and giving you cookies, to the point where you were wrapping and reselling them at the market, don't you think you should do something for them in return?
Not if they gave me a legal document explicitly stating I didn’t need to give them anything…and I could get an infinite amount of the cookies with no extra work or money on their part…
And I would probably suggest to them that if they were interested in profiting from their cookies they should stop giving them away for free and make them commercial instead. They might then tell me they don’t want to spend the effort and money to commercialize their cookies, or maybe they prefer it as a hobby with no obligations to customers, or maybe they tell me they have a philosophical belief that they should give their their cookies away for free for anyone to do as they please with them, including commercializing them as long as they aren’t legally responsible for anything done with the cookies which is why they handed me that legal contract explicitly stating that when they gave them to me in the first place.
Yes but thank-yous are always good. Making sure the project sticks around is just smart.