I am shamelessly swiping this article from my co-worker Dave Voyles from this page.
Xamarin, the group behind the Mono, the open source implementation of Microsoft’s .NET framework, have done it again, but this time, in the gaming space.
With Mono for Unreal Engine, you can now use the latest version of C# to write your gameplay code, AI behaviors, UI elements, and more.
You have access to the entire range of capabilities of the .NET framework, up to version 4.5. You can even use C# async programming to author your code. Download it and give it a try.