Stack Exchange is described as 'Fast-growing network of 84 [and counting] question and answer sites on diverse topics from software programming to cooking to photography and gaming. We are an expert knowledge exchange: a place where physics researchers can ask each other about quantum' and is a very popular Q&A service in the education & reference category. There are more than 50 alternatives to Stack Exchange, not only websites but also apps for a variety of platforms, including Self-Hosted, Android, iPhone and Android Tablet apps. The best Stack Exchange alternative is Quora, which is free. Other great sites and apps similar to Stack Exchange are Codidact, Aether, Tildes and WikiSpooks.com.