C Sharp

Running C Sharp code in web browser

Blazor

Blazor is open source web framework, which can compiles C# to WASM and then it can run in a web browser.

External links

https://en.wikipedia.org/wiki/Blazor

Bridge.NET

Bridge.NET is a open source C# to JavaScript Compiler.
Official website (dead link): http://bridge.net Archived at: https://web.archive.org/web/20210502211824/https://bridge.net/
Bridge.NET is no more under active development.
There is a fork of Bridge.NET named H5. Its Github repository is: https://github.com/curiosity-ai/h5

JSIL

JSIL is a compiler that converts .NET applications and libraries from CIL bytecode into standards-compliant JavaScript, which can run in any modern browser or JavaScript runtime. Unlike other JavaScript cross-compilers, JSIL generates JavaScript that is easy to debug while preserving the original .NET code's behavior and structure. Supporting most .NET-based languages, it works seamlessly with C# and VB.NET, with partial support for F#. The compiler handles nearly all .NET runtime features, including pointers and P/Invoke, and can translate most of the open-source Base Class Library (BCL).

Official website: http://jsil.org/