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.
Phabricator - Phacility - Phabricator
Atlassian Crucible - Collaborative peer code review tool.
BitBucket - Bitbucket is a free code hosting site for Mercurial and Git. Manage your development with a hosted wiki, issue tracker and source code.
Storybooks.io - UI code reviewing done right
Gerrit Code Review - OpenSource Git Code Review Tool