Gallica is one of the major digital libraries available for free via the Internet. It provides access to any type of document: printed documents (books, press and magazines) in image and text mode, manuscripts, sound and iconographic documents, maps and plans.
The French Revolution Digital Archive (FRDA) is a multi-year collaboration of the Stanford University Libraries and the Bibliothèque nationale de France (BnF) to produce a digital version of the key research sources of the French Revolution and make them available to the international scholarly community.
Stereoscopy is a technique for creating the illusion of depth by presenting two images (usually photographs) to the eyes, each one taken from a slightly different perspective (often about the same distance apart as human eyes). The resulting images, when viewed through a stereoscope, appear three-dimensional.