They do own it. Any court would likely agree that what OpenTTD does is copy an IP they own. And they'd have the right to C&D it.

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JoshTriplett 3 hours ago | parent | next [-]

Reverse engineering for compatibility, and implementation of a compatible system (as long as you don't copy the original) are not just legal, they're explicitly legally protected in many jurisdictions. You'll get in serious trouble if you copy the original, but there is specific case law supporting things like emulators. See, for instance, Sony v Connectix and Sega v Accolade.

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gmueckl 3 hours ago | parent [-]

But OpenTTD is explicitly a faithful copy of the original. It replicates the original product in appearance and behavior and is open about it. If you were to dig into source code history, mailing list archives, chat logs etc. I'm certain that you could find a lot of evidence to support this position.

	▲	JoshTriplett 3 hours ago \| parent \| next [-]
		"Behavior" isn't copyrightable; it explicitly isn't, in fact. To what extent did they copy "appearance" other than supporting the use of the original assets? It is certainly possible that they didn't scrupulously maintain clean hands, but I wouldn't automatically assume that.
	▲	einr 2 hours ago \| parent \| prev [-]
		GNU’s Not Unix is explicitly a faithful copy of UNIX. It replicates the original product in appearance and behavior and is open about it.

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Cthulhu_ 2 hours ago | parent | prev [-]

It's... complicated; they own Transport Tycoon Deluxe, its code, its assets and its IP.

Back when OpenTTD first released, it was a decompile (?) of TTD that loaded the assets of the game itself. This was... legally dubious, since reverse engineering.

But over time they Ship of Theseus'd the game - all code rewritten from assembly to C/C++ (I don't know), open source asset packs, etc. It's still the same base game, same feel, etc but nothing of the original code or assets remain.

I don't know enough about IP law etc to judge whether Atari would have any leg to stand on in a court of law, but it would be Complicated to say the least.