Regional Transportation District bus stop import
The Regional Transportation District (RTD) is a public transportation agency in the Denver, Colorado, metropolitan area. In 2013, RTD bus stops were imported from the agency's GTFS feed by 
release_candidate (on osm, edits, contrib, heatmap, chngset com.).
License
RTD's license agreement allows redistribution but the agreement is revocable. Instead, Derek Kniffin reached out to RTD directly to obtain a clear statement that:
RTD has no objections to geodata derived in part from RTD's GIS data being incorporated into the OpenStreetMap project geodata database and released under a free and open license
Nevertheless, the imported bus stops are tagged license=http://www.rtd-denver.com/Developer-licenseagreement.shtml. This accounts for the vast majority of occurrences of license=* in the OpenStreetMap database (as opposed to the OpenHistoricalMap database, where this key sees more widespread usage).
References
- Kniffin, Derek (August 26, 2013). “RTD Denver GIS data”. imports mailing list.
- Kniffin, Derek (August 30, 2013). “RTD's GIS Data in OpenStreetMap”. imports mailing list. [1]