A list of free skateparks in the US.
The website collects some data, as it has google analytics, but it seems that there are no ads. The free skateparks they point to might have some rules like:
Skateboarding and roller skating only, Helmets, elbow pads, wrist guards and knee pads required, Only city-installed equipment may be used in the skating area or adjacent park area, Use of tobacco, alcohol or drugs is prohibited, No food or drink allowed in the skating area, No glass items permitted, No graffiti, stickers or littering, No profanity, Skate at your own risk
So I don’t know – the rules want you to behave a certain way, but I’d say most of them are so called “common sense” to make sure that people don’t damage the place, leave dangerous items behind like glass and that people use this place in a safe way (use helmets, treat each other well etc.). From my experience these “rules” are written on a sign in front of a skatepark and you can stick to them or not – it’s not that you won’t have access to them if you don’t wear a helmet. So from my subjective view I won’t consider these as macro-trades, but maybe it is different with some of these and they are controlled and if you don’t wear a helmet you won’t have access, which would be definitively a macro-trade and thus not trade-free. So I give 3 out of 5 blocks because the website collects data.