|Stable branch, features a DBus interface.
|Unstable branch, defines what will be the 2.0.x stable series, features the DBus interface and other design improvements over 1.4.x.
|Old stable series, features an XML interface.
Latest code (git)
To get the latest development code, you can do:
$ git clone git://anongit.freedesktop.org/git/system-tools-backends.git
Alternatively, you can visit the FreeDesktop gitweb to view the repository through the web browser.