Closest SC4 sucessor for now is the game "New Cities" that is fundamentally different, and proprietary.
Open Source there is an early SimCity clone, but it is not a clone of SC4 specifically, and it is a lot more simple.
There were multiple attempts by multiple people on starting such projects, but all of them failed fairly early, the task is seemly just too daunting, in fact this is part of the reason why the game got released in a unfinished state, in an interview a programmer that worked on SC4 at the time said they "coded themselves into a corner", and were unsure how to fix it, EA then gave them the ultimatum of "release now or never", reimplementing SC4 itself thus seems to be too hard.
OpenTTD was much easier, in part because TTD itself was written in assembly, so when you decompile it, you are seeing the actual source for most part, there are no C++ craziness going on, no virtual tables or crazy jumps.
SC4 was written in C++ with a ton of non-standard stuff, Paul Pedriana is a mad genius, so unless you have supernatural amounts of patience and time, you won't understand a disassembly of SC4, you need the source to do anything substantial.
Closest SC4 sucessor for now is the game "New Cities" that is fundamentally different, and proprietary.
Open Source there is an early SimCity clone, but it is not a clone of SC4 specifically, and it is a lot more simple.
There were multiple attempts by multiple people on starting such projects, but all of them failed fairly early, the task is seemly just too daunting, in fact this is part of the reason why the game got released in a unfinished state, in an interview a programmer that worked on SC4 at the time said they "coded themselves into a corner", and were unsure how to fix it, EA then gave them the ultimatum of "release now or never", reimplementing SC4 itself thus seems to be too hard.
OpenTTD was much easier, in part because TTD itself was written in assembly, so when you decompile it, you are seeing the actual source for most part, there are no C++ craziness going on, no virtual tables or crazy jumps.
SC4 was written in C++ with a ton of non-standard stuff, Paul Pedriana is a mad genius, so unless you have supernatural amounts of patience and time, you won't understand a disassembly of SC4, you need the source to do anything substantial.