Bolero is a set of tools and libraries that enable F# applications to run in WebAssembly using Blazor. It provides HTML functions with a syntax similar to WebSharper.UI or Elmish.React, as well as templating functionality to write HTML in a separate file and bind it to F# using a type provider. Bolero also offers Elmish integration, allowing users to run an Elmish program as a Blazor component and Blazor components as Elmish views. Other features include routing, remoting, and F#-specific optimizations to reduce the size of the served application.