DPLA collects information about digitized resources from institutions all over the country so that all of their content can be searched through the single DPLA interface.
A local partner of DPLA, Digital Commonwealth provides a similar service for collections held by institutions in Massachusetts.
Digitized materials from the collections of the world's largest library, an agency of the U.S. government's legislative branch.
Check the "Available online" box when searching, then click "Freely available" under the Availability options on the results page (in the left margin).
