General
The RoadMap
Tips for ContributingChanges
OptionNaming - the conventions used to name command-line options
WritingTests - how to add tests to the test suite
DeveloperRepos - where to find various public repositories of Mercurial work
CategoryNewFeatures - A page of links to discussions about new features.
NewIdeas - Suggestions for features/extensions that would make someone happy
- A list of ["Presentations"] and other related events.
Mercurial Internals
- ["Design"] - Mercurial's data structures and how it uses them.
WhatGoesWhere - the project architecture
WireProtocol - the push/pull changegroup protocol
DebuggingFeatures - how to poke around in Mercurial's internals
- ["Theming"] - how to create new styles for Mercurial's web interface
ExtensionHowto - how to write Mercurial extensions
RequiresFile - capabilities check for repositories
Old Stuff
First Mercurial UserSurvey.
The old ToDo list and MissingFeatures
Ideas for Google's SummerOfCode2006.