See https://www.mediawiki.org/wiki/Wikimedia_Release_Engineering_Team/Project/Differential_Migration for more context and timeline.
Goal: The goal is to get about 1 project per WMF "team" and a couple "community-owned" projects.
Purpose: To get people using Differential at a slower pace of adoption in the beginning instead of all at once. This will allow us to help them and respond to issues more quickly/effectively and increase the number of people who can help others when the time comes (eg: their other project collaborators).
Repositories:
Projects already using Differential: