...is a build and debugging tool based on sbt.
It is used to coordinate the development of multiple, independent projects that evolve in parallel: dbuild uses a multi-project definition file to build all the requested projects, and makes sure that they all work together, even though each of them may evolve independently.
You can find the complete dbuild documentation at the dbuild web site.
dbuild is now only used by the Scala 2 community build. It receives only light maintenance, as needed, from the Scala team at Lightbend.