Distributed Version Control System.
Eric Sink notes: Industry-wide, there is a trend toward more integration between version control and other stuff like project tracking, TeamWiki-s, Discussion Forum-s, build tracking, etc. (Issue Tracker, Software Forge) Developers don't just checkin code. They use a whole bunch of other tools which help them collaborate with each other and with people in other functional areas. While DVCS is one of the more interesting things happening right now, it does represent a setback in this particular area. The benefits of a DVCS are somewhat diminished if all of the other tools a developer needs are still "centralized"... As far as I know, Fossil (Fossil SCM) is the only tool which is a DVCS with bug tracking built-in. But it is not the only project exploring this area of need.
He also said But if I were choosing a DVCS as a regular user, I would choose Mercurial. I've used it some, and found it to be incredibly pleasant. It seems like the DVCS that got everything just about right.