You can access the CircuitPython Web IDE at : https://mr-coxall.github.io/CircuitPython-IDE/
The goal of this project is to develop an IDE specifically for CircuitPython that will work on all systems (OK all systems that run a Chrome browser). The Mu IDE is wonderful but in particular it does not work on Chromebooks. You can use the Chromebook's built in text editor, it even has syntax highlighting, but there is no REPL so debugging is really, really hard.
The intent is to have a super simple and lightweight IDE that can be used on any device that has a Chrome browser. Maybe even small enough so it could be kept right on the CircuitPython device itself!