Development Methodologies & Security:
Test-Driven Development (TDD), SonarQube (for quality code analysis)
Agile/Scrum methodologies
API security and WebSocket security
I'm a drop out from school. All my technical skill are through asking stackoverflow.com. Not until I found hacker news, I got the best tools to use, have a community that supports the site. And overall, I never end the day without opening it.