I don't think there is any fundamentally original idea in replit.
It is a time-sharing system where you can log in and use a programming language.
We have had those since not long after the dawn of computing.
Since at least 1970, we also had smart terminals that allowed the user to fill in a form, and validate it, before sending it to the host.
So the time-sharing session being carried out by a protocol between the web front end and back-end is not ipso facto original.
Needless to say, neither is the idea of a repl running in a separate process that provides editing, with expressions sent out to a running image for evaluation.
It is a time-sharing system where you can log in and use a programming language.
We have had those since not long after the dawn of computing.
Since at least 1970, we also had smart terminals that allowed the user to fill in a form, and validate it, before sending it to the host.
So the time-sharing session being carried out by a protocol between the web front end and back-end is not ipso facto original.
Needless to say, neither is the idea of a repl running in a separate process that provides editing, with expressions sent out to a running image for evaluation.