Some resources for those studying philosophy, critical theory, etc.:

ARISTOTLE

A reconstruction of Aristotle’s Protrepticus by D. S. Hutchinson and Monte Ransome Johnson

LEIBNIZ

Leibniz texts online

KANT

Akademieausgabe von Immanuel Kants Gesammelten Werken

HEGEL

A Hegel reading list

Hegel, The Letters, trans. Clark Butler and Christiane Seiler

MARX

A Marx reading list

Karl Marx / Friedrich Engels Papers at the International Institute of Social History (Amsterdam)

MEW (all volumes as PDF)

THE VIENNA CIRCLE

Scientific World-Conception. The Vienna Circle (‘manifesto’ of the Vienna Circle, 1929)