CSS Guidelines is a document created by Harry Roberts. Guidelines and profound advice for writing sane, manageable and scalable CSS.
Shrthnd – easy to use CSS shorthand web application. You just have to simply input standard CSS and the app will output a shorter version. It will help you keep your style-sheets small.
Best thing about this, that is free, with it you can create a typographic system with vertical rhythm and modular scale.
Its one of the best places to deploy AngularJS, Ember, and Backbone apps.
draGGradients – create custom #CSS radial-gradients by simply dragging their mouse.
Exercism – online portal for users to engage themselves in thoughtful conversations about code thereby improving software development.