[OrangeMusic]

I'm pretty sure that making new software that replicate the _functionality_ of other existing software is perfectly legal.

If not, how do you explain the thousands of Tetris clones? The thousands of Doom clones? The hundreds of Excel clones (forgot which was the first one, it's not Excel but that's besides the point, which is that's perfectly legal). Another commenter already mentioned Android SDK vs Java, which Oracle (fortunately) lost.

Yes, even the "copywriting" is fair game, unless it's pages and pages of text (e.g. don't copy/paste the documentation).

The design mustn't be identical but if it's essentially identical, that's legal - sometimes there aren't 10 ways to do something.

Now if the question is whether it's legal to publish software written by LLMs, given that they've been trained on other people's code - that's an entirely different question.