Forest Extension
This extension is not being distributed along with Mercurial. It's being developed by Robin Farine and can be downloaded from its [http://www.terminus.org/hg/hgforest public development repository].
Overview
The Forest extension allows operations on trees with nested Mercurial repositories, called forests. It provides commands that apply to the forest. These commands are both standard Mercurial commands, such as 'clone' or 'status', and commands that involve a snapshot file, to represent the state of a forest at a given time.