Codacy - Automatically reviews code style, security, duplication, complexity, and coverage on every change while tracking code quality throughout your sprints.

Coverity Scan - Find and fix defects in your Java, C/C++ or C# open source project for free

CodeClimate - Code Climate provides automated code review for your apps, letting you fix quality and security issues before they hit production. We check every commit, branch and pull request for changes in quality and potential vulnerabilities.

SonarQube - SonarQube, a core component of the Sonar solution, is an open source, self-managed tool that systematically helps developers and organizations deliver Clean Code.

Embold.io - Peer Code Review

Feram - Feram finds bugs in your merge requests and suggests patches to fix them.