From the Delft Technical University, this list of Open Educational Resources is a great starting point for finding Open Access Educational Resources. After opening the pdf you can go to the individual websites via the icons with each item.
Other open educational resources
UN-Habitat learn: water and sanitation, the environment, urban management, land and housing, slums, and women’s rights.
A NUMBER OF OPEN TEXTBOOK INITIATIVES
A NUMBER OF OPEN E-BOOK INITIATIVES
The National Academies Press (USA): Sciences, Engineering and Medicine
InTech Open: multidisciplinary scientific literature
The World Bank Open Knowledge Repository: research and knowledge products on development.
Food and Agricultural Organization of the UN: all FAO publications full text online
Directory of Open Access Books