ClusterTruck, an upcoming first-person 3D platformer being developed by Landfall Games, and published by tinyBuild, currently has a free alpha build available for download.
ClusterTruck is a storyless physics-based platformer based solely around jumping across moving trucks in order to get to the end of each level without touching the ground once. The movement and the behavior of the trucks is altered slightly based on where and how you land on them, which creates a system where pattern memorization in order to get to the end of a stage is not an option. This makes the game a fairly unique take on a challenging platformer.
You can watch a recent trailer for ClusterTruck right here: