Uxcel - The easiest way to learn UX/UI design
LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
PixelSnap - Measure every pixel on your screen with ease ✨
whatdevsneed - This is whatdevsneed.
UXsniff - Track user behavior on your website and improve conversions with UXsniff: the user experience watchdog that looks out for you.
SmallDevTools - Handy developer tools with a delightful interface