OpenStreetMap (OSM) was started in 2004 largely motivated by the expensive and restrictive licensing of the government spatial data available in the UK at the time. Since then OSM has defined crowdsourcing in the geospatial domain.
August 9th 2004 was the day that the first user registered the domain and started the project. I blogged about March 16th, 2009 when the 100 000th user registered on OpenStreetMap. On January 6, 2013, OpenStreetMap crossed the one million users mark. The number is currently about 1.1 million registered users. (OSM are careful to point out a majority of users are casual or inactive, with a small minority contributing the majority of additions and corrections to the map.) When the number of users hit 750,000 the number of active mappers was about 24,000. More than 1,000 new mappers contribute every day. New edits appear on the map in about a minute. In 2007 this took a week.
Initially OSM used a Creative Commons license, but OSM now has its own data license which it moved to on April 1st, 2012.
According to the just released 2013 OpenStreetMap Data Report, OSM's database now contains 33,968,739 km (21,107,196 miles) worth of road data. It also contains 78 million building footprints. That's about 3.2 billion GPS points.
A new in-browser map editor was just released on OpenStreetMap.org. The new editor is designed to improve the first-time editing experience while providing a fast and intuitive interface for everyone mapping on OpenStreetMap.