The new garbage collector that we're currently developing called Garbage First or G1 for short. G1 straddles the young generation - tenured generation boundary because it is a generational collector only in the logical sense. G1 divides the heap into regions and during a GC can collect a subset of the regions. It is logically generational because it dynamically selects a set of regions to act as a young generation which will then be collected at the next GC (as the young generation would be). G1 can choose the regions with the most garbage to collect first (Garbage First, get it?) so gets the biggest bang for the collection buck.
(c) Jon Masamitsu, Our CollectorsThat G1 is now a part of JDK 7.