The Acme editor is sort of like that. Text frames you can drag around and organize with the mouse. You can run commands that get their own frame for output, you can launch a shell in a frame and interact that way, you can browse directory structures, and of course you can edit files. I don't think it's what you're thinking of (Oberon, maybe?) but you might find it interesting: https://research.swtch.com/acme