One of my first scala projects, "http://tryscala.com" had a good run from 2010 - 2017. There are other good options now, https://scalafiddle.io comes to mind, so I'm retiring it - don't visit the address, not sure what you'll find there now!
It was an online scripting/fiddle tool for scala, with content assist, short URL fiddles, forking etc. Here's the screenshot of how it looked before I deactivated it:
You could edit the code and see the result right there, fork it etc.
Many of its features morphed into DieselApps and the diesel project.
See also the original Scripster github project