Mercurial (or popularly, hg) is a DVCS written in Python. It is known for its ease of use, without compromising a lot of power.
See parent wiki page Action items for moving Drupal.org off of CVS for more generic information.
- Mercurial has excellent Windows support and this was the major reason git was not Mozilla's choice for their DVCS.
- Mercurial is just cool and can do the same.
- Mercurial commands are very similar to cvs/svn (unlinke git), and it supports only a single workflow (unlike bzr) which simplifies support
- The Mercurial community rocks, and is always ready to provide support in #mercurial on Freenode
- Mercurial supports pulling over http and pushing over https (I know at least 1 of the other contenders does as well) this simplifies the process and doesn't require ssh keys to be managed, just standard http auth, which can be performed against a database easily
- Converting from CVS is simply
hg convert drupalwhere drupal is a CVS checkout. This can be re-run as necessary to keep the HG repo in sync with upstream changes. <- interesting. Can this also keep a hg checkout in sync with git/bzr? if so, can't hg users continue to use the workflow they're used to no matter what vcs drupal.org switches to? - Mercurial features an excellent patch management system called Mercurial queues, or MQ. It is an included plugin, and allows the management of multiple dependent patches, and can even version the patches themselves.
Drupal (module and theme) developers are mostly not hard-core developers and the joy factor is very important. Mercurial delivers that. Git is created for Linux and developing for kernel automatically makes you hard-core developer that uses Linux. But web developers are very different and good Windows/Mac support is a must.
(start writing points already!)