My editor https://webide.se/ https://webide.se/ use operational transform for undo/redo, collaboration, and code replay for macro and tutorials. I think Heroku

My editor https://webide.se/ https://webide.se/ use operational transform for undo/redo, collaboration, and code replay for macro and tutorials. I think Heroku also started out as an editor, but pivoted to "code-execution as a service".