The implementation hasn’t drawn me over to it yet, but I think the mathematic-pioneered concept of mixing output (including graphics) with input is fantastic,
It wouldn’t work with TextMate though, as it requires formatting text and graphics inline…
The TM approach, I think, would be a linked window, full of formatted and foldable output, but with a distinct text-only window to drive it. Perhaps with cursor mapping from a click in the formatted doc.
I’d pay $49.99 for that implemented cleanly and maintained like RStudio is, with export to pdf web etc working properly.