Quoting from https://en.wikipedia.org/wiki/Phabricator

  Phabricator was originally developed as an internal tool at
  Facebook. [0][1][2]

Companies using Phabricator [3]:

  - Stripe
  - Pinterest
  - Khan Academy
  - Asana
  - Wikimedia Foundation
  - KDE
  - Dropbox
  - Uber
  - Bloomberg
  - Deviant Art
  - Haskell.org
  - Babel JS
  - Facebook
  - Instagram
  - MemSQL
  - Disqus
  - FreeBSD
  - Blender

[0] https://secure.phabricator.com/book/phabflavor/article/proje...

[1] http://techcrunch.com/2011/08/07/oh-what-noble-scribe-hath-p...

[2] http://readwrite.com/2011/09/28/a-look-at-phabricator-facebo...

[3] https://www.phacility.com/