Frameworks are more like collection of ready to use standard Components that solve some kind of common web design problem which otherwise would require CSS, JS or HTML authoring from scratch. Frameworks is one of useful front-end developers tool for faster and better development. With frameworks you can build a well structured, maintainable and up-gradable website. It also helps you save much on your time because there are plenty of readily available elements that you can use.
Bootstrap :
Bootstrap was developed by Twitter developers and released for public use in 2011 as open source framework. As of today, Bootstrap is the most used front end web development framework in the world.
Bootstrap is a powerful frontend development framework that includes HTML, CSS and JS components for building mobile first responsive websites of all sizes and complexity. The best thing about Bootstrap framework is that it is continuously upgraded by the bootstrap developers with latest technological advancements to solve complex web design problems of modern times. Recently, Bootstrap was upgraded to utilize Sass as the CSS preprocessor, Sass is the most used and feature rich CSS preprocessor.
Foundation:
Foundation is most likely the toughest rival for Twitter Bootstrap. It is very well documented, stable, flexible and open source front-end framework. It has many useful tools for creating responsive, mobile first web project faster. It supports almost all the available browser today, except for IE7. Although many developers are mostly using Foundation for HTML and CSS only, but you have option to port it with Sass and Rails.
Gumby:
Gumby is a flexible and responsive framework built with the power of Sass for faster web development. Its customizer allows you to easily tweak and customize the entire UI kit design to meet your best preference. Gumby has multiple types of grids with different column variations, but by default, Gumby comes with 960 grid system. You get modern look and feel for buttons, forms, indicators, navigation, tabs, tables, tooltips, icons and almost any design component you would need in modern times.
Pure:
If you are planning to build a web app that works both on desktop and mobile, then you should consider of using Pure from Yahoo. Pure has much better performance when it comes to mobile devices than Bootstrap. As its name suggests, Pure comes as a pure CSS framework only. Build on top of Normalize.css, Pure has an extremely small file size with just 4.5KB. Pure is a light weight package of CSS modules that can be utilized in any web project.
Skeleton:
Skeleton is a lightweight CSS framework that uses a 12-column grid system. Unlike Bootstrap or Foundation, Skeleton provides you with some fundamentals components only like button, lists, table, forms which aimed to kick-start your development process. Skeleton is a small collection of css files that can help you rapidly develop sites that look beautiful at any size.