Are you aware of the AEGIS (Africa-Europe Group for Interdisciplinary Studies) series published by Brill? The books in this series are available open access (with an embargo of two years).

The African Studies Library (also known as “Fachinformationsdienst Afrikastudien” in German) has recently licensed an e-book package from the African Books Collective. Registered users have access to a searchable database of more than 1500 titles from African publishers.