This is an extensive and well-organized site featuring "high-quality historical resources for teachers and students for free and without advertising," a feat accomplished through partnerships with a variety of museums and archives. In addition to primary-source material, including multimedia, the site, which is presented in the form of a digital textbook, features resources such as an interactive timeline of U.S. History from 1590-present, subject guides, handouts, and lesson plans. Users are also invited to direct questions to the "Hyperhistorian," Steven Mintz, John and Rebecca Moores Professor of History at the University of Houston. The archives of these queries and answers are accessible as well.
This site will be especially useful for high school and post-secondary level history instructors and students.