Introducing organization webhooks
github.com/blog/1933-introducing-organization-webhooks
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
Webhooks are now available at the organization level on GitHub.com. Organization webhooks send events for all repositories in an organization. They also include new events for repository creation, team membership, and more.