Among modern, distributed VCS systems, the closest VCS system to Mercurial is Git. Some differences between Mercurial and Git are the following:

• Multiple, built-in undo operations: Mercurial’s revert, backout, and rollback commands make it easy to return to previous versions of specific files or previous sets of committed changes. Git provides a single built-in revert command with its typical rocket-scientist-only syntax.
• Built-in web server: Mercurial provides a simple, integrated web server that makes it easy to host a repository quickly for others to pull from. Pushing requires either ignoring security or a more complex setup that supports Secure Sockets Layer (SSL).
• History preservation during copy/move operations: Mercurial’s copy and move commands both preserve complete history information, while Git does not preserve history in either case.
• Branches: Mercurial automatically shares all branches, while Git requires that each repository set up its own branches (either creating them locally or by mapping them to specific branches in a remote repository).
• Global and local tags: Mercurial supports global tags that are shared between repositories, which make it easy to share information about specific points in code development without branching.
• Native support on Windows platforms: Mercurial is written in Python, which is supported on Microsoft® Windows® systems. Mercurial is therefore available as a Windows executable (see Resources). Git on Windows is more complex—your choices are msysGit, using standard git under Cygwin, or using a web-based hosting system and repository.
• Automatic repository packing: Git requires that you explicitly pack and garbage-collect its repositories, while Mercurial performs its equivalent operations automatically. However, Mercurial repositories tend to be larger than Git repositories for the same codebase.