UI kits
Similar to CSS frameworks, there is another type of frontend framework called UI kits. However, UI kits can be a breed of their own.
Truth be told, sometimes differentiating between a CSS framework and a UI kit is difficult. But don't delve too much into which one is which, the important thing is to understand why we're using them in the first place and how they can help us build better and faster responsive sites and apps.
The following list describes some of the features and characteristics of UI kits:
There are basically two types of UI kits: those that are built with web technologies (HTML and CSS) and can be used to prototype web-based applications, and those that are made of (usually) Photoshop (PSD) files to help mock up and design native mobile apps.
Very few web-oriented UI kits offer a grid of some sort.
UI kits are focused on providing user interface components such as sliders, paginations, navigation bars, dialog boxes, overlays/modals, buttons, typography, tooltips, lists...