... I send out a list of most interesting libraries and apps in the "CSS" section to about 1100 subscribers.
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ReX CSS Framework Documentation
A beautiful CSS framework designed for minimalists.
Superdesk UI Framework
PUXL framework is a free and open-source and eco-friendly library to create front-end Web interfaces. It helps you build accessible and responsive sites with lightweight HTML.
Web UI framework, Apigee style: a set of common styles and (eventually) widgets for web apps and static pages.
List of awesome CSS frameworks