Rktcr (from "rocket car", pronounced /ɹktkɹ/) is a physics-based side-view action-platformer-turned-puzzle-platformer; that is, it's an action game meant to be played thoughtfully at much slower than real-time.
Rktcr is tool-assisted-speed-run: the game. Players can see the future and control the flow of time, allowing them to play frame-perfectly. Paths through levels can be easily shared, for boasting or collaboration.
Rktcr contains 37 challenge levels, ranging from easy to impossible; and 31 world levels, algorithmically arranged into 300 worlds of varying complexity. All told, there are more than 1600 paths to discover and optimize.
Demo3 contains a selection of challenge files along with a single sample world. I expect it should take about 1-2 hours to finish, and strongly recommend starting with the challenge files.
Note: Rktcr will run in a 1280x720 window by default; this is configurable in-game (F10). If you can't get to the config menu, you can also change the resolution by editing the "~/.rktcr/rktcr.conf" text file (OSX and Linux) or the "%UserProfile%\Documents\rktcr\rktcr.conf" text file (Windows). This file will be created when you first run the game.
Learn To Play
Level packs are zip files containing extra challenge levels. Unzip, then copy the (non-readme) files into your "rktcr/userlevels" directory. If you've created levels you'd like to see here, let me know.
Meditations on Bouncing by ix (September 6th, 2013). Five challenge levels built around the notion of getting the perfect bounce; from vertical, horizontal, and diagonal walls.
(Also available via Desura, though I would prefer you to use the humble store widget above, and you'll get a Desura key anyway.)