Lightweight (~11KB Zip Archive)
Designed for mobile first
Based on Flexbox
Open source on github
More concise syntax. The Class names are short and easy to remember. You don't have to struggle with remembering the names, just add the row class and then the number of columns you want.
With Uncaught.css there is no need to load an extra js file. For components like modal, toggle Navbar etc. that requires JavaScript to function, their code snippet are included in the docs so you just copy the code instead. Which makes it is very easy to integrate in any JS environment.
The Fontawesome 4.7.0 library is already included in the uncaught.css file, but you can always upgrade it to that latest version, or use any other icon library if you want.