What small tool, web or Windows, do you keep searching for?

I’m launching AppErgo this Saturday 👋 AppErgo started with just a handful of tools and has grown into a collection of 200+ free online tools.

Before launch day, I’d love to ask: what kind of small web tool do you find yourself searching for again and again? And which web tools would you find useful as small standalone Windows apps?

It can be something very simple or oddly specific. I’m always looking for genuinely useful ideas rather than adding tools just to increase the count.