Horner works in the area of Open and Collaborative Resources. His Fellowship enables him to work on a number of projects in this area. Horner manages the Siyavula project, where he co-ordinates the development of a comprehensive set of Open Educational Resources (OER) supporting the South African National Curriculum. This relies on the development of communities to create and support the OERs as well as the provision of platforms for development. Horner believes in the liberation of information and supporting education in South Africa. He is one of the co-founders of the Free High School Science Texts
project, launched in 2002, and founder of FullMarks, launched in 2010.