f.lux changes the color temperature of your screen. Nothing spectacular so far, but it adjusts to the local day time. It’s a nice effect, especially early in the morning or late in the night — maybe not the proper tool for graphic designers or people in need for accurate colors.
Nocturne however follows a different path, a more nerdy adjustment. Instead of changing the color temperature, it adjusts to certain color modes, like negative, red/green screen, etc. It isn’t of much use at day time, but it shines at night or better … it gives you proper night vision ;-)