Mercurial is the only version control system that I actually like, and I do celebrate each time I see a project use it. So, here I list the most notable projects I am aware of that do, which also gives me hope that it isn't being suffocated too much by Git:

  • Firefox, world number 3 desktop web browser (number of users)
  • OpenJDK, the top open source implementation of the Java platform
  • Netbeans, one of the most popular IDEs

And here is one which is not FLOSS (i.e. proprietary):

  • Facebook, world number 2 website in terms of visitor numbers