Hi rjurney. I would say "Hive, Pig, Cascading" are on the higher level API side and "Pangool, MapReduce" on the low-level side. Pangool is a MapReduce API that aims to make MapReduce simpler. We explain this better in our FAQ: http://pangool.net/faq.html
HIVE -> Pig -> Pangool -> Cascading -> MapReduce
Nice addition!