The editor of TMNF is very simple and powerful, letting you create any track that you have played in the game. Using a simple system of track pieces and props, you create a Hot Wheels-esque stunt track that might be very tough and narrow and slow to navigate, maybe you make a nice fast track with wide turns and many turbo-boost tiles, or perhaps you infuriate the player with a 30 minute track of death and crazy stunts that are almost impossible to complete to reach the next stage of the track floating 300 feet in the air. All of these and any combination therein is possible. But the real gems as I have discovered, are the press-forward tracks.
I find Press Forward tracks to be the result of "playing" the TMNF editor. The editor is so easy to use and it is so easy and simple to test, that people create a piece of track, press forward and see where their car goes. Then they create some more track and add a jump. Then they see where their car goes. Then they build track up in the air where their car ended up. Then they start adding more and more pieces and creating a maze of speed. This is really easy too, and it all hinges on two simple factors: testing is almost instantaneous and there is no randomness in TMNF's physics. It is beautiful.
Press forward tracks are like movie-making, but even more satisfying, in my opinion. To play a track is fun. It might be almost exactly like watching a youtube clip of a PF track, but there is a very interesting dynamic in the player always needing to press forward. Play one of the best tracks and then stop pressing forward at some point. You screw it all up and you feel as if you are backstage at Disneyland.
Press forward tracks are an interesting phenomenon created by Trackmania's wonderful and intuitive editor. I have spent more time with Trackmania than almost any other game (and it's free!). Check it out sometime, and consider the editor and what it has done. It has created an intricate alternative Rube Goldberg-machine-maker.