The W3C cheatsheet provides quick access to useful information from a variety of specifications published by W3C. It aims at giving in a very compact and mobile-friendly format a compilation of useful knowledge extracted from W3C specifications, completed by summaries of guidelines developed at W3C, in particular Web accessibility guidelines, the Mobile Web Best Practices, and a number of internationalization tips.
Its main feature is a lookup search box, where one can start typing a keyword and get a list of matching properties/elements/attributes/functions in the above-mentioned specifications, and further details on those when selecting the one of interest.
The W3C cheatsheet is only available as a pure Web application.