Stack Overflow is described as 'Part of Stack Exchange, is a free, community-driven, reputation-based Q & A site for computer programmers. No membership is required to ask questions or provide answers to questions by others' and is a very popular Q&A service in the education & reference category. There are more than 25 alternatives to Stack Overflow for a variety of platforms, including Web-based, Self-Hosted, Android, Linux and Mac apps. The best Stack Overflow alternative is Quora, which is free. Other great apps like Stack Overflow are Codidact, TopAnswers, Scoold and GeeksforGeeks.
Unlike most of the other alternatives here, which either are Q&A boards that are general-purpose and not focused on programming, antiquated software/platforms, or simply wrappers of SO. solvin however is a direct, focused alternative that's far more welcoming and helpful.