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

Free Code Camp - Learn to code by helping nonprofits.

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.

W3Schools - W3Schools is a web developers information website, with tutorials and references on web development...

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.

Codecademy - Learn the technical skills you need for the job you want. As leaders in online education and learning to code, we’ve taught over 45 million people using a tested curriculum and an interactive learning environment.