Opal-playground is a jsBin like webapp, but with an Opal focus. It inclues other things like a built REPL via opal-irb.
To show opal-irb, press the 'Show Irb' button
To hide opal-irb, click on the red 'X'
There are 2 slide out sections
The left slide out, also toggle-able from the help button, gives help and a way to show the compiled code. Click on the > to open, and < to close
The right slide out shows the results of compilation after 'Run Code' is performed. Compile errors willl show here as well. Click the < to open and the > to close