Mercurial is:

Fast
  • Extremely high-performance delta-compressed [:Revlog:storage scheme]

  • Optimized for disk layout and access efficiency
  • Complete cross-indexing of files and [:ChangeSet:changesets]

  • Bandwidth and CPU efficient HTTP and SSH sync [:WireProtocol:protocols]

Scalable
  • Distributed development model supports unlimited numbers of developers
  • Allows arbitrary [:Merge:merging] between developer [:Branch:branches]

  • Doesn't significantly degrade with large numbers of files or changesets
  • No waiting for locks!
Robust
  • SHA1 integrity checking on [:Repository:repository] data

  • Append-only storage model with transaction journalling
  • Fast full-repository verification
  • Convenient [:BackUp:backup]

Easy to use
  • Most commands are familiar to users of [:CVS] and other systems
  • Built-in command help
  • Integrated stand-alone web interface
  • Works with various [:GUIClients:GUI tools]

Easy to adopt
  • Runs on UNIX, MacOS X, and [:CategoryWindows:Windows]

  • [:RepositoryConversion:Conversion tools] available for many popular [:SCM:SCMs]

  • Allows a variety of [:WorkingPractices:usage models]

  • Supports user-defined [:Hook:hooks] and [:CategoryExtension:extensions]

Free
  • [:DeveloperRepos:Source code] available under the GPL license

  • Actively [:MailingLists:community] supported and [:DeveloperInfo:developed]