Social networking and career profiles/portfolios for software and web developers and designers. Automatically aggregates content from open-source project hosts, other social networks, e-learning and learn-to-program sites, app stores, etc.
The official CSS page at the W3 Consortium.
The "Learn & Use" page is crammed full of links to tutorials, articles, and events. The majority of resources are in English, but there appear to be a decent number in other languages as well.