Mecurial is an open-source version control application. It's free and written in Python.
Ranked in these QuestionsQuestion Ranking
Pro Easy to use
Mercurial is a more intuitive option than many of its competitors. The documentation is well organized and easy for beginners to read & understand.
Pro Free and open source
Mercurial is open source and free to use.
Doesn't require access to a central repository, because each checkout is a full repository by itself.
Mercurial is designed to make performing operations (such as commits, clones etc.) fast.
Pro Good documentation
Mercurial documentation covers everything from revision control system basics to mercurial specific features in a short and clear way.
Pro Fully python based
Pro Same features Git provides, but much easier to use and to understand.
The command-line interface is more intuitive, requiring much less memorization and exotic options/piping to achieve the same thing you would in git.
Pro Native Windows support
Native Windows support. No trace of cygwin or other dirty hacks typically found in competitors.
Pro Doesn't delete history
Mercurial makes it pretty darn hard to delete history by mistake. In Git, if you mistakenly commit to HEAD and switch to a different branch, your commit is toast. Yes, you can dig through the reflog but most users don't even know of its existence and will wish they didn't once they find out.
Pro Actively contributed to by Facebook
Mercurial is actively contributed to by the developers at Facebook as they use it for their massive source repository.
Con Lost the widely adopted race to git
Sharing code and projects in an open source world is a must and trying to working with multiple Source Code Control systems does not help the ecosystem.
Con Can't delete named branches
You pretty much have to use tags instead.