Hackr.io - There are tons of online programming courses and tutorials, but it's never easy to find the best one. Try Hackr.io to find the best online courses submitted & voted by the programming community.
Bootstrap 4 Cheat Sheet - An interactive Bootstrap 4 cheat sheet
Programming Hero - Personalized, fun, and interactive way to learn programming
Bootstrap Zero - Open-source, free Bootstrap templates collection.
BigTube - Makes watching programming tutorials more fun
HackerThemes - Bootstrap 4 themes and tools for web developers