Regardless of where you find information, it is important to evaluate the source of it, especially if you are using it for decision-making or in an educational setting.
This page has been built to point mostly to authoritative sources (excepting the “general purpose” section), however sources should always be examined carefully.
Practically every library has a tutorial on this so I will simply point to evaluating sources on Google; most of the results there are good tutorials.
Search Engines and Directories
The first three tools listed in this category are directories compiled by consortiums of universities.
ipl2 was formed from the merger of two prior academic directories, the Internet Public Library and LII, Librarians’ Index to the Internet.
iSEEK and Virtual LRC are more like traditional search engines, but similarly limited to preselected academic sources.
These search engines include papers and other academic documents, largely from academic journals.
I have focused on search engines which include the most papers and provide direct access to them, rather than simply listing the citations.
Most of these are built partially or wholly on OAI-PMH,
a standard enabling organizations to share information about the documents they include.
If you are looking for journals themselves, rather than their articles, you should instead be using the academic search engines.
Online Courses and Video
The first two sources here are for finding online courses. The OpenCourseWare consortium includes courses offered freely online from MIT and many other institutions of higher education.
Udemy is more informal and includes some of these but also courses contributed by their users.
The remaining sources are all for online video of an educational nature. Note that all of these sources are also available on the Video Search Engines page.
Flashcards and Quizzes
These are all websites which have large libraries of existing flashcards and make it easy to study online, and in some cases print off the information to study offline.
Smart.fm and Flashcarddb both use some form of spaced repetition which is a method of presenting flashcards or other information at the best times to improve memory retention.
There are many other websites and prorgrams which support spaced repetition, such as those mentioned in the Wikipedia article.
These tools allow you to find books, and in some cases from Open Library, Google Books, Amazon, and the Hathi Trust, access some or all of the book online.
Note that these sources include all sorts of books and include fiction as well as academic books.
Docs and Presentations
These are both general-purpose websites which allow anyone to upload word processor documents and presentations, many of which are informational.