These are platforming maps made to enhance your Overgrowth reflex skills. Overgrowth is required to play. To download and play, simply log in on the Wolfire website and find the thread WolfBrother9393's Platforming Maps and follow the instructions on the thread.
Don't watch if you want to be able to play and solve the map yourself. This video is a demonstration and guide through my level, Garrison, which you can download and play here: Forums.wolfire.com . This map focused more on puzzle elements than platforming fidelity but that's what makes it so fun!