Europeana 1914-1918 is a portal project of Europeana, itself a digital portal, too, to bring together resources, both texts and images from all corners of Europe. Special attention is given to materials hitherto hidden away or especially brought to attention for this portal by the general public. Among the documents are letters, diaries, photographs (including stereographs, mostly from the Imperial War Museums), official documents, films, sound recordings and postcards. One of the strong new features is the integration of materials from Australia, New Zealand, Canada and the United States. You can also search for the various fronts. Europeana 1914-1918 had in 2014 an interface in fifteen languages, currently (2018) you can choose from 27 languages.
The films available at the European Film Gateway 1914 can be found here, too. Collections from many European libraries and other cultural heritage institutions are also present at the portal Europeana Collections 1914-1918.