ErikZalm/Marlin — pull request #548 by buildrob101 (2013-07-20 03:22:59+00:00)
Title: Added dual x-carriage support

Using dual x-carriages allows some significant improvements in dual extrusion printing as you can park and cap one extruder while the other is printing. This avoids the problem of the inactive extruder oozing on the print.
You can see an example here: http://www.thingiverse.com/thing:115885