Marxists Internet Archive
Society, Politics, Socialism, Theory - Marxists Internet Archive. The most complete database of Marxism hitherto made.
https://www.marxists.org/
Working Class Movement Library
Society, Politics, Socialism, Theory - Working Class Movement Library. A collection of materials concerned with the activities, expression and enquiries of the labor movement, its allies and its enemies, since the late eighteenth century.
https://www.wcml.org.uk/