All these books are free to read: either they're distributed with a free license, or they're in the public domain.
Douglas Wilhelm Harder et al.
Aya Homei and Michael Worboys
Suzanne Conklin Akbari (editor)
Jane McKenzie et al.
Mahmoud Mohieldin and Djordjija Petkoski, editors
The Univalent Foundations Program, Institute for Advanced Study