There are several websites with different types of primary sources but this is my favourite. Fordham University has published a "collection of public domain and copy-permitted historical texts presented cleanly (without advertising or excessive layout) for educational use".
It has three main collections: Ancient, Medieval and Modern. In each collection you can find subsidiary sections such as Absolutism, Byzantium, Celtic states, and Egypt, to name a few. What I also like about this website is that categories are cross-referenced. So if you clicked on "Medieval" you will find the category "Renaissance" there as well as in "Modern".
Subcategories are quite diverse. You will find groups of sources that may talk about Persian religions, Hunter-Gathering societies, Late Ancient Philosophy, Science and Technology in the Middle Ages, Women in the Middle Ages, Everyday life in Modern Europe, Australia and New Zealand, and Pop culture.
It also holds other sourcebooks on topics such as women, Indian, Jewish, African, East Asian, Lesbian/Gay, Science, and Islamic history. Moreover, there is a list of special resources on Byzantium, Medieval times, and saints' lives.
I hope you find it useful!
