freeCodeCamp is a non-profit that teaches coding for free through interactive lessons, certifications, articles and YouTube videos, with a large community of learners.
DEV Community is a social network and blogging platform for software developers, where members share posts, tutorials and discussions, and it is built on the open-source Forem software.
Stack Overflow is a question-and-answer site where programmers ask and answer technical questions, with voting and reputation, and is one of the largest developer communities.