A quick glance at Xamarin Workbooks, a cross platform .net sandbox that lets you easily write and execute .net code anywhere.
Xamarin Workbooks let you write code for Console, WPF, Android or iOS applications and display the results. This can range from the most basic Hello World to complex 3D renderings (more about this here: https://developer.xamarin.com/guides/cross-platform/workbooks/samples/tinyrenderer/).
The tool is still very much in its infancy but it’s a good cross platform alternative to the Mono REPL or LINQ Pad.
Want to play with Xamarin Workbooks? Get it for Windows, MacOS or Linux here: https://developer.xamarin.com/workbooks/
Check out LinqPad as well! http://www.linqpad.net