1. Apache Hadoop: http://hadoop.apache.org.
2. Apache PigMix: http://wiki.apache.org/pig/PigMix.
3. Apache S4: http://incubator.apache.org/s4.
4. Asymptotic analysis of self-adjusting contraction trees: http://www.mpi-sws.org/~bhatotia/publications.
5. Storm: http://storm-project.net.