Set Culture of the thread to the same as the browser.
This way the client gets the same date formating as his computer..

Add Nemerle language: http://nemerle.org

Add Support shortcuts for build and e.g. like in Visual Studio

Would be cool to be able to use named union fields, as detailed here: http://blogs.msdn.com/b/fsharpteam/archive/2013/06/27/announcing-a-pre-release-of-f-3-1-and-the-visual-f-tools-in-visual-studio-2013.aspx

Sometimes it is nice and handy to write a stuff and download it not messing with csc

Include the UnityEngine Library so we can test Unity C# scripts.

In order to practice streaming files and reading from files to demonstrate well written code, you need the ability to upload at least a .txt file to work with. How about you allow .txt files to be uploaded for this purpose?

It would be nice to be able to login in mobile version to see "My Fiddles".

This is a very essential feature as people are used to hit F5 to run code, and instead all their work is gone.
Please also show a confirmation message if user clicks the browser refresh button.

Console.WriteLine($"{i} ");

throws error: Compilation error : Unexpected character '$'

It'd be nice if the FSharp script template would print out return values, especially since those used to FSI expect it, and the C# script template does.

You can share your code but there is no option to look up others code.

Please create mobile app for this wonderful service. It may help lots of people where accessing laptops or systems is not easy.

Need to support following:
1. Set of predefined coding questions asked
2. Should log number of attempts the user tried (like logging number of time Run button is clicked)

It would be very useful to be able to search for existing fiddles under a particular tag. Like 'Rx" fiddles.

Add exporting the fiddles externally to visual studio.