@rubenwardy Interesting, I did not hear about this until now.

I was actually looking into the true origin of OpenTTD a while back out of personal curiosity and what seems to have happened was that Ludde took the raw disassembly (the game being written purely in assembly making that a lot easier to pour through than something generated from an optimising compiler), translated it into higher-level C code, wired it up to SDL for cross-platform support and then put a GPLv2 license on it. Not really a clean room reimplementation approach.

I guess this is not too dissimilar to modern game decompilation projects which have generally remained up in code form despite producing 1:1 binaries of games (there's no way they do not look at the game's disassembly!) from litigious companies such as Nintendo. However when I was reading old Transport Tycoon forum threads I found a funny remark about how OpenTTD is entirely legally above board because the only person who had been exposed to the original TTD disassembly was Ludde, who lives in Sweden - the magical middle land where copyright does not exist! (Not their exact words, but I have seen similar sentiment elsewhere well into today's age. It's not true.)

I'm glad that Principia has seen a better post-commercial fate. Things looked bleak for a while before the open source release, but now we're truly free.