Earlier quoted context omitted.
(In some cases a donation button may be better) If you are not a charity, do not call it a donation. Call it a tip .
Is there some legal distinction? Getting money with the expectation that it will be used to further some vaguely defined public good you are doing (writing freely available software in this case) sounds exactly like a charity, especially since you will be doing most of the public good regardless of whether you get the donation or not. A tip on the other hand is an additional payment for some good or service that you…
Tip signals "payment for my work." Donation signals "gift."
People seem to be more inclined to actually fork over a few bucks if you signal "This is my work. I deserve to be paid for it." than if you signal "I would like gifts (or charity) from random internet strangers."