This is an awsome web game. It´s easy to play and some video examples on YouTube shows that there is no limit for your creativity.
Link of latest version (web based game).
Download this version (beta 2) and first version (you will need flash player instaled): Beta 2 | Beta 1
Line Rider was originally created by Boštjan Cadež, a Slovenian university student, in September of 2006. It almost immediately gathered a cult following and became the seventh quickest gaining keyword in Google. Since that time, the ‘toy’ has generated over 16 million views. Fans quickly noticed that they could create tracks, set them to music, and share them over YouTube.com (source: official-linerider.com).
Some crazy videos examples:
viciei!!!!!