The UI aesthetics look similar to the excellent Rill, also powered by DuckDB: https://www.rilldata.com/
Rill has better built in visualizations and pivot tables and overall a polished product with open-source code in Go/Svelte. But the DuckDB UI has very nice Jupyter notebook-style "cells" for editing SQL queries.
Rill founder here, I have no comment on the UI similarity :) but I would emphasize our vision is building DuckDB-powered metrics layers and exploratory dashboards -- which we presented at DuckCon #6 last month, PDF below [1] -- and less on notebook style UIs like Hex and Jupyter.
Rill is fully open-source under the Apache license. [2]
[1] https://blobs.duckdb.org/events/duckcon6/mike-driscoll-rill-...
https://youtu.be/_IqvrFWY7ZM?si=1ux9SGUsh4kDs-ff
Alongside several great talks including Rusty Conover presenting Airport - Arrow + DuckDB — and Christophe Blefari (Bl3f) introducing a new, lightweight orchestrator called yato.