Playgreen is no longer maintained and its owners cannot be contacted :-(. However, the mission continues at Appropedia.org.
Appropedia covers green living, sustainable technologies, appropriate technology, tackling climate change, etc. There are articles about articles growing food, yardsharing, resilient communities, greywater treatment, sustainable housing and more.
It is also a friendly community.
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Sustainability wiki pioneers missing
What happened to the good folks who started Playgreen? Please let the people at Appropedia know if the Playgreen folks are still interested in their vision for a knowledge base on sustainability - they would be happy to collaborate.