Gerrit Code Review - OpenSource Git Code Review Tool
LightReview - Simple, but powerful code review system for small teams.
Phabricator - Phacility - Phabricator
Upsource - Upsource provides unified access to all your projects stored in Git, Perforce, Mercurial or Subversion.
GitHub - Originally founded as a project to simplify sharing code, GitHub has grown into an application used by over a million people to store over two million code repositories, making GitHub the largest code host in the world.
Code Collaborator - Learn more about CodeCollaborator, the industry's first code review tool.