Here are a few examples:

  http://trafficserver.apache.org/
  http://developer.yahoo.com/yql/
  http://github.com/yahoo
  http://yuilibrary.com
  http://developer.yahoo.com/yap/guide/caja-support.html
  http://developer.yahoo.com/yslow/
  http://developer.yahoo.com/search/boss/
  http://developer.yahoo.com/hadoop/