EBSCOhost is a major database platform with over 30 databases indexing scholarly, popular, and news content in the social sciences, humanities, and sciences. EBSCOhost databases can be searched simultaneously.
Google Scholar searches across academic disciplines and resources for scholarly literature. Though its algorithm (the "page rank" engine thing that drives the search) is uniquely Google, Google Scholar in fact resembles other academic or scholarly research databases (search tools) that allow the researcher to search through a very large index to scholarly material from a single platform.
"Project MUSE is a leading provider of digital humanities and social science content for the scholarly community." Access the complete, full-text versions of scholarly journals from many of the world's leading university presses and scholarly societies, with over 120 publishers currently participating."
ProQuest is a major database platform with over 50 databases indexing scholarly, popular, and news content in the social sciences, humanities, and sciences. ProQuest databases can be searched simultaneously.
"Annual Reviews critically reviews the most significant primary research literature to guide researchers to the principal contributions of their field and help them keep up to date in their area of research. Each article is its own search engine, providing a gateway to the essential primary research literature referenced within each topic."
"JSTOR currently includes more than 2,000 academic journals, dating back to the first volume ever published, along with thousands of monographs and other materials relevant for education."