Hello, apologies for the self-promotion but I’m building a tool called Radix which is a knowledge work harness. It’s similar to Feather (that you linked) but imho a stronger tool. Please email or message me if you would like to give it a try for free instead of paying the subscription price.
Hm. Same as with the other guy, looking at your screenshots, I'm left with a kinda "eh" feeling.
So there's a side pane and a main section and a text input.
Very..uh.. plain. I was envisioning some more specific UX flow, but I couldn't tell you how, exactly.