Search your notes, PDFs, and code, citing the source; check for questions, progress, and quizzes.
Free
One server, in learning & documentation. Search your notes, PDFs, and code, citing the source; check for questions, progress, and quizzes.
Learning & Documentation
Search your notes, PDFs, and code, citing the source; check for questions, progress, and quizzes.
The rest either hold an API key issued by the publisher or ask for nothing.
Listed without a verification tick. Read the listing before installing.