OAIster

Uses the Open Archives Initiative (OAI) protocol to gather over 23 million records of free, useful, wide-ranging digital resources hosted at over 1,100 institutions. Covers resources of all kinds, including digitized books and articles, born-digital texts, audio files, images, movies, datasets, theses, technical reports, research papers, etc. All records contain a digital object link allowing users access to the object in a single click.

Varies by resource