Project Gutenberg is an online library over of 70,000 free eBooks. They focus on materials whose U.S. copyright has expired; in practice, this mostly means books that were first published at least 95 years ago. More recent translations are unlikely to be available here as the translation has its own copyright.
From the Bibliothèque nationale de France, this resource contains over 2 million digitized items including manuscipts, books, and other material. Some navigation is available in English, but much of the content and the website are only in French. French philosophers, and those with substantial connections to France or French philosophical movements, are the primary focus.
Europeana is a collection of digitized material from libraries, archives, and museums all across Europe.
Past Masters contains 117 fulltext humanities databases, both in the original language and in English translation.
Nietzsche Source has digitized works, manuscripts, letters, and other documents from the Nietzsche Estate.
Wittgenstein Source provides digitized manuscripts and other materials from the University of Bergen and other Wittgenstein collections.