Nightdive Studios

Nightdive kept the original System Shock available next to its remake. Nightdive released the original System Shock along with its source code, so players could still get the original while a heavily changed remake existed.

The reasoning is that games get stuck on dying hardware, get delisted, or lose servers, so some players depend on a remake as the only way back. Big changes work best when the original stays available. The source frames this as a preservation issue: "it just means we need better game preservation".