Lately, there has been a large amount of fan-made demakes that bring modern games to classic consoles, and the latest seeks to bring a first-person game to a console famous for first-person shooters.
Portal fan James Lambert is working hard to bring the Valve classic to the N64, and you can see the progress in the videos below.
This game is running on actual N64 hardware, and not just trying to mimic the look of the system. If you want to keep up with the project, more details can be found here.