Opal Developer Tools od Jan Biedermann

Opal Developer Tools provide a console to interact with a Opal Ruby Web Application to aid development and debugging.
Instructions for getting the Object Browser working are on the github page.
Open source, MIT License: https://github.com/isomorfeus/opal-devtools
Part of the Isomorfeus Project. For more information see: https://isomorfeus.com.
More information about Opal: http://opalrb.com