I'm pretty sure CPython reference counts objects. Also Objective-C -- as in GNUStep, if you aren't using a Mac server.

EDIT: There's a downside to reference counting in that either you or the runtime does the retain/release calls very often, whereas a mark-and-sweep collector would just touch each object once per collection. So reference counting might not be faster overall, but typically avoids long pauses. What you probably really want is something like Azul's JVM, which has a kernel extension so they can collect memory concurrently, resulting in shorter pauses than sweeping and faster overall time than reference counting.

We employ a technique similar to that of Obj-C in our memory handler implementation. You attach objects not to a parent object, but to a generation. We have 4 a-priori-specified generations per node (2 of them are stubborn and die during the de-initialization/clean-up phase of the node as a whole).

And this is another area where a functional paradigm makes sense. Mutations are "hidden" (and the C layer that's responsible for doing them concurrently lives in another "realm" (monad)). So, memory handling is easy and monitoring has shown us that fragmentation is kept to a minimum.