A user naively snitching on the project between their 2nd and 3rd posts is a really great bit.

Snitching? Talk about making a tiny email a big deal. Atari already knowing about OpenRCT2 since before the email makes the forcible induced drama even more cringy.

I was involved in the early days of OpenTTD and one of the big issues was the first version was basically just a decompiled version of the original TTD binaries. Giving any kind of blessing would basically relinquish control of IP - that due to publisher contracts he may or may not actually be able to do. Legally this is the only thing he can say.

Why would implementing a compatible game engine be unlawful? The code he wrote is copyrighted but the concepts and functional elements embodied by his code shouldn't be protected.

OpenRCT2 and OpenTTD are, at best, derivative works, if not outright infringement (the line between infringement and derivative in computer code is quite muddy, and there is very little in the way of precedence to illuminate the difference). These projects are not like WINE or ReactOS, reimplementing something by carefully observing what it does and attempting to reproduce it, but rather built (originally) by decompiling the original and otherwise heavily reliant on outright reuse of parts of the original.

OpenRCT2 was a direct derivative of RCT2 at first, to the point it would just directly call into the game executable everywhere.

See e.g: https://github.com/OpenRCT2/OpenRCT2/commit/643db7ae017e04d1...

I see. Yeah it's hard to defend that. The correct way to do it would be to reverse engineer the game and produce a clean room implementation.

That isn't derivative. That's a plugin. At that point if OpenRCT2 is calling into the original, intact binary, there can be no infringement. You're just running the executable as provided and your computer just so happens to have another program running in the same memory space.

I'm unfamiliar with OpenRCT2 but I can't imagine the RCTC rebuild has nearly as many features; them making the comparison just makes their project look worse.

It has feature parity, and more. It's an incredibly faithful recreation to the original - and the features they have added in my opinion are primarily QoL improvements and nothing stupid.