Available both on YouTube and on Crunchyroll:

http://www.crunchyroll.com/shelter/shelter-porter-robinson-presents-shelter-the-animation-722793

Shelter tells the story of Rin, a 17-year-old girl who lives her life inside of a futuristic simulation completely by herself in infinite, beautiful loneliness. Each day, Rin awakens in virtual reality and uses a tablet which controls the simulation to create a new, different, beautiful world for herself. Until one day, everything changes, and Rin comes to learn the true origins behind her life inside a simulation.

Made me cry ;_;

Also, somebody here posted a translation of the letter at the end of the video:

http://tinyurl.com/zl88tgn