This is a card in Dave's Virtual Box of Cards.
A Forth IDE
Stack-based "concatenative" programming can be a real beast to visualize in my head. I think a simple terminal IDE might be very usable with just a few features:
Auto-complete or lookup of dictionary words (showing stack effects and reflecting current stack state!)
Always-on summary of available memory, S0, HERE, etc.
In addition to a terminal IDE, if a WASM Forth is possible, the browser could be a fantastic host for a Forth IDE. (Insert dictionary words by simply clicking on them, etc.) Heck, you could even do some amazing diagrams and stuff with canvas.