PLUTO is a comprehensive land use dataset for New York City that was made free to the public in 2013.
Building and address data was joined with PLUTO to color over 1,000,000 buildings by their recorded date of first construction. This data was then overlaid on OpenStreetMap roads and rendered into a static tileset using Mapnik.
Featured in The Atlantic Cities Blog.
Also see research on erroneous building ages at Brooklyn 11211.