Every developer should have a sketch book. Their own, simple, comfortable environment for building prototypes & experiment with ideas. A free space. No CI, no linting, no tests, no restrictions.
It's not just for personal projects. Working at a startup taught me that not every business need is worth implementing into your production system. Some features are not used often enough to justify the extra effort or complexity. Sometimes you just want a quick prototype.
Your sketchbook can contain different mediums, too. Some things are fine just being CLI scripts.
If you want to host your sketchbook somewhere and allow others to interact with it, maybe make it a simple site and expose behind a VPN or password-protected reverse proxy like Caddy. I highly recommend server side rendering and htmz for this exact use case. I avoid complexity in my sketchbooks, and any kind of transpilation and project templates is complexity. If you really need lots of client-side interactivity, you can use vanjs or preact.
Need visualisations? You can use css for basic bar graphs/tables, or pick up Vega Lite, or Plotly, or Matplotlib.
Pick a popular language that you feel comfortable in (JS, Python) or use something you really like (Clojure? Elixir? Go) as long as it doesn't slow you down.
Using SQL databases in your startup? Have a ready to go usage example for querying them.
Inspired by: An app can be a home cooked meal.