The docu of the external DAM Module (https://docs.magnolia-cms.com/product-docs/6.2/Connector-Packs/DAM-Connector-Pack/External-DAM-module.html) mentions only 3 official integrations: S3 and Bynder. However there seem to be many more, as can be seen under https://documentation.magnolia-cms.com/display/SERVICES/Incubator 

Even if some do not have official releases yet, it would be a good idea to at least mention them.