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

2009
Smarter Cities and Flawed Rankings
Alex Steffen critiques the current practice of ranking cities on sustainability with data that is "easily measured, but sort of pointless" and looks forwards to a time when city rankings judge a city "not by its neighbors, but by what's needed to save the planet"...

2008
The Complexity of Sharing Scientific Databases
Ethan Zuckerman explores the complexities of applying the Creative Commons concept to science, and examines the Science Commons project...

2005
Ad Hoc Network Leapfrogging
Jamais Cascio writes that CUWiN -- the Champaign-Urbana community WIreless Network -- brings together a bunch of worldchanging ideas into one useful package: Free/Open Source software to create ad-hoc municipal wireless networks using recycled old PCs...

Other recent "look backs":
July 13
July 14
July 15