Looking back one, two and five years ago today on Worldchanging:

2009
Nothing for today!

2008
A Whole Different Kind of Green Roof
Alex Steffen shares images that he likes from the FreakAngels series...

2005
If You're Looking For Me, You'd Better Check Under the Sea
Jamais Cascio looks at SEA-LABS, a student-designed project to use low-power wireless transmission to monitor coral reefs in real-time -- and the technology could be applied to any remote undersea sensor scenario...

Other recent "look backs":
June 3
June 4
June 7