Legend has it Sunsoft, the company that made Batman for the NES, was developing a Superman game. The Lost Levels has an article about Sunman, another unreleased NES game that looks like a Superman game, but stars an unknown solar powered hero who happens to have the same powers as certain Kryptonian.
Now a build of the Superman game is out, also graciously provided by the Lost Levels team. Download it here. Then punch enemies out of existence and zap a helicopter with laser eye power.
What is Sunsoft doing these days? Releasing tile matching mahjong games and original manga on WiiWare.