Yes, Nut is a fork of https://bolt.diy and like bolt.diy you can add your own API key and use it as much as you want (Nut is hosted though so you don't have to set anything else up).

The improvements we're making are under the hood. When you ask Nut to fix a bug it should do a much better job -- we record the app's behavior and analyze it so the AI has context for the changes it needs to make.

We've also added some UI to approve or reject the changes the AI makes. For now we're using this to gather feedback so we can improve Nut, but down the line we'll also refund the user any credits when they reject changes -- you shouldn't have to pay when the AI screws up, a big issue with these tools (and vibe coding in general).