What are the best tools you’ve discovered over the years?

Let’s share hidden gem tools, not the usual stuff that shows up in every "top developer tools" post, but smaller tools and projects that made you think, "wait, this is actually really useful." I'll start with 3 I've come across: 1. Archify https://github.com/tt-a1i/archify Found this recently. It's an agent skill that works with Claude Code, Cursor and Codex and basically turns a codebase into an interactive architecture map. You can export it as HTML/PNG/SVG/WebM, and one thing I thought was pretty cool is that you can diff the architecture before a merge to see how a PR changes the system. 2. boneyard-js https://boneyard.vercel.app Generates skeleton screens from your actual UI instead of making you manually recreate the layout with placeholder components. Pretty nice alternative to manually maintaining react-loading-skeleton stuff. 3. Gradient Studio https://gradientsaas.blogspot.com Simple procedural CSS gradient generator. Has stuff like mesh gradients, aurora effects and grain. You mess with the settings and copy the result as CSS, Tailwind or SCSS. I've been using it mostly for quick landing page backgrounds. What's one tool you keep recommending that somehow still isn't very well known?