Check https://github.com/JoystickAndCursorKeys/hyperpetscii/wiki for more information.
HYPER PETSCII is a PETSCII editor with a twist. Instead of using a modern GUI to allow you to edit the PETSCII graphics, it takes you back in time, and gives you access only to a GUI made directly in the C64 graphics mode (right in the web browser). (But with a dual monitor setup, something the C64 did not have).