Understanding open source architectures I

https://github.com/foursquare
https://code.google.com/p/foursquared/wiki/Design
https://code.google.com/p/foursquared/source/browse
https://sites.google.com/site/foursquareddev/ux/venueactivity

https://github.com/foursquare/Android-PullToRefresh
https://github.com/foursquare/SlidingMenu

Eclipse:
http://www.aosabook.org/en/eclipse.html

Graphite:
http://www.aosabook.org/en/graphite.html

http://www.tornadoweb.org/

http://blog.reddit.com/2008/06/reddit-goes-open-source.html

https://code.google.com/p/guava-libraries/wiki/GuavaExplained