The SAFE stack—short for Suave, Azure, Fable, and Elmish—brings a number of technologies into a coherent stack for web development. It's built around the F# programming language, both on the server side and in the browser, and therefore has a focus on functional, type-safe programming with an asynchronous approach. It offers productivity features such as hot reloading and lets you substitute parts of the stack, for example, the server-side web framework or the cloud provider.