It looks like Repl.it is in this thread, they might provide an exact answer.

But, if they don’t, here’s my take. To me it seems like this is something that would be built in-house with the ability to leverage repl.it’s existing application infrastructure. I’d imagine this would simplify the development compared to the vscode plugin. (stand-alone desktop app)

Also, long-time gitlab-CE user here. I’d love to see multiplayer as a feature.