Wren - Offset your carbon footprint by saving rainforests
Vibe Boost - An interactive digital museum of video-based art.
Neutral - Offset your carbon emissions, right from your shopping cart
Mixergy - The YC Stories - How YC companies - Airbnb, Dropbox and more - Got Started
Trip to Carbon - A carbon footprint calculation API for travel.
Endangered Sounds Museum - Nostalgic sounds from the past