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.
Beyond Compare - Beyond Compare allows you to compare files and folders.
Codacy - Automatically reviews code style, security, duplication, complexity, and coverage on every change while tracking code quality throughout your sprints.
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
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.
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.