"Do you have any examples of projects where the solution was somewhat vague and open-ended"

This one is pretty open ended, and I'm having a ton of fun designing and iterating on it: https://github.com/simonw/claude-code-transcripts - it's also attracting quite a few happy users now.

I have another project in the works in Go which is proving to be a ton of fun from a software design perspective, but it's not ready for outside eyes just yet.

"Did you feel excited or energized by having an LLM implement these projects end-to-end"

I'm enjoying myself so much right now. My BART rides have never been this entertaining before!

"Do you think others would find these projects useful? In particular, if you vibe coded them, why couldn’t someone else do the same thing?"

I don't think many developers have the combined taste and knowledge necessary to spin up Denobox or django-transactions. They both solve problems that I'm very confident need solving, but I expect to have to explain why those matter in some detail to all but a very small group of people who share my particular interests.

The other two are pretty standard - I suggest anyone who wants to learn more about JavaScript interpreters or WASM runtimes try something similar in the language of choice as a learning exercise.