"Terms of Use" are part of the agreement between you and a service provider with regards to the service being provided. That's a civil law contract like any other.
No that's not, and I'm not playing on semantic. Laws are above any terms of use, regardless of what they might say. And not using the product makes you not bound to the terms of use, unlike laws which you have to obey at all times.
I'm beginning to think that when you said by "not signing anything" earlier, you actually meant "not agreeing to anything", is that correct?
> And not using the product makes you not bound to the terms of use, unlike laws which you have to obey at all times.
Of course not. But in this specific case, it is safe to assume that he is using the product, or more specifically: he used Slack to develop BetterSlack.
Regardless of where you are, the majority of the agreements you enter into are not only not signed, they are not even explicit (but rather implied).
Case in point: practically everytime you buy something and pay with cash, you have entered into a purchase agreement without having signed anything.