Mercurial is:

Fast

  • Extremely high-performance delta-compressed storage scheme

  • Optimized for disk layout and access efficiency

  • Complete cross-indexing of files and changesets

  • Bandwidth and CPU efficient HTTP and SSH sync protocols

Scalable
  • Distributed development model supports unlimited numbers of developers

  • Allows arbitrary merging between developer branches

  • Doesn't significantly degrade with large numbers of files or changesets
  • No waiting for locks!
Robust

  • SHA1 integrity checking on repository data

  • Append-only storage model with transaction journalling
  • Fast full-repository verification

  • Convenient backup

Easy to use

  • Most commands are familiar to users of CVS and other systems

  • Built-in command help

  • Integrated stand-alone web interface (example)

  • Works with various GUI tools

Easy to adopt
Free