I spent some time last week working on a free CSS boilerplate I'm calling Shoelace.css. It's kinda like Bootstrap, but a lot leaner and pure CSS. You don't need a preprocessor like Sass or Less to use it, but it's still highly customizable with CSS variables.
I'm calling Shoelace a "starter kit", not a framework. The goal was to create a lightweight, fully customizable, and extensible boilerplate for building websites and web apps.
What makes Shoelace really awesome is that you can
<link> to it with just one line of code and start using it. Customizations can be made in your own stylesheet by simply overriding variables:
For more info and to grab the source, head over to shoelace.style.