Preboot is a great collection of LESS utilities (variables and Mixins). It is an improvement from bootstrap. This is the best and most powerful tool for CSS development.
This is an online tool that can help to extract ids, classes and inline styles from an HTML document and output them as a CSS style sheet. All you have to do is to type or paste your HTML document and let extractCSS do the rest for you.
Formoid is an amazing tool that helps creates advanced and attractive web forms. With a no-coding drag-n-drop GUI, trendy Flat, Metro, Bootstrap form themes, pure css styled, responsive, retina-ready form elements are readily available.
Topcoat is another great tool for css. It is a clean and fast web app. It provides more useful features as themeable, BEM architecture, free fonts, icons, designs, components galore and much more.
Create CSS3 is an online tool with inbuilt code and functions.
Tridiv is a web-based editor for creating 3D shapes in CSS.
CSS type set provides a facility to type text that you want to modify and find the CSS-generated sheet to your style sheet.