A provider of online maps and contributor to many popular online mapping libraries and applications.
Mapbox offers commercial mapping services. Many of them use OpenStreetMap data and involve large open-source efforts. Mapbox is a main contributor to the Mapnik renderer project, they helped create the web editor iD and they created Tilemill, the software used to design the OpenStreetMap map style. (from http://wiki.openstreetmap.org/wiki/Mapbox)
Mapbox was created as a part of Development Seed in order to offer map customization for non-profit customers, in 2010. It was bootstrapped until a 2013 $10M funding round by Foundry Group. Early work on OpenStreetMap tools, including the iD editor, was funded by a $575,000 grant from the Knight Foundation. (from http://en.wikipedia.org/wiki/Mapbox)