Here are links to some annotated directories and bibliographies, specialized libraries of online sources and other online resources. Organized from multidisciplinary to specialized.
https://www.ascleiden.nl/content/library
Searching in the publication databases of Connecting-Africa https://www.connecting-africa.net and AfricaBibhttps://www.africabib.org
https://library.columbia.edu/libraries/global/virtual-libraries/african_studies.html
Official “WWW-Virtual Library guide for African Studies” is a part of (the first) virtual library World Wide Web Virtual Library.
Database of journals published in Africa.
Database of journals published in Africa, including archival publications.
http://libguides.lib.msu.edu/africa
Annotated list of sources, including multimedia.
https://www.aodl.org/
https://www.oxfordbibliographies.com/obo/page/african-studies
Annotated bibliographies.
http://library.stanford.edu/africa-south-sahara
Annotated directories.
https://www.internationalafricaninstitute.org/repositories
List of digital repositories (according to countries)
Africa currently, social sciences, literature
http://bcea.cei.iscte-iul.pt/en/
The library provides Portuguese materials from academic institutions focused on Africa.
Africa currently, social sciences.
https://baslerafrikabibliographien.faust-web.de
https://www.bodleian.ox.ac.uk/weston/finding-resources/guides/commonwealth_african
British colonial historical sources (correspondence, documentation)
https://africaneuropeanarratives.fcsh.unl.pt/
https://www.africamuseum.be/en/research/collections_libraries
Central Africa