The number of free (or low cost) online tutorials for developers to learn programming today is outstanding. Never before have learning resources been so easily accessible.
My favorite type of tutorial are the interactive style where you get to work on a solution to a problem online and the site checks your result and gives you feedback. Compared to a static tutorial where you just read materials or watch a video, this additional interactive step really helps to apply your understanding at a practical level.
(NOTE: list in progress – last updated 11/03/20)
These are some of my favorite interactive learning resources: