Gerrit Code Review - OpenSource Git Code Review Tool
Approved - The better way to get approvals, right inside of Slack
Phabricator - Phacility - Phabricator
Approve app for Zendesk - Any enforceable and auditable approval workflow for Zendesk tickets you can imagine can be easily created using the Approve app.
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.
ApproveIt for Slack - Get approvals in minutes, not days. Right from Slack!