This page details pretty much all I use as a developer. If you decide to make your own, consider adding it to Wes Bos' uses.tech. I use a Mac, so most tools are macOS specific, but there are some OS-agnostic ones in the list. You might also be interested in My Mac Setup post, although it is a little outdated.
xScope - Awesome toolset for frontend development. Rulers, guides etc.
Dato - A better date app for macOS. It's great for having multiple time zones in the address bar. I have my local time as well as UTC. I also use it for upcoming meetings and events. Previously I was using Meeter which is great for this, but it's one less app I need now.