jikes
MMTK
A garbage collection framework similar to the plai2 framework but less designed as a "toy" is the mmtk(Memory Management Toolkit) for the jikesRVM.
A quick overview of the interaction between the virtual machine and the mmtk framework can be found here: http://jikesrvm.org/Memory+Allocation+in+JikesRVM
Jikes is surprisingly both non-frightening and full-featured. One of the surprising things about MMTK is the presence of such optimizations as thread-local allocation interfaces while still retaining the simplicity of the memory manager interface.
If you're planning on making a collector for jikes, I believe that the best overview of the way that the collector is expected to be structured and how Jikes will use it can be found here: http://jikesrvm.org/Anatomy+of+a+Garbage+Collector
It comes with a large number of garbage collectors. They all satisfy a simple interface which captures the information that a collector needs.
Many of them will implement this interface, so it's worth looking at for the curious: http://jikesrvm.org/docs/api/org/mmtk/plan/Simple.html
There is a fairly straightforward tutorial on adding a simple mark-sweep collector and a quasi-generational hybrid copying/mark-sweep collector here: http://jikesrvm.org/MMTk+Tutorial
And I was glad to see that there was a comprehensive test harness for jikes. One of the most difficult things with plai2 is figuring out how to test things in isolation and together, and how to track test program misbehavior to a specific collector fault. http://jikesrvm.org/The+MMTk+Test+Harness The harness looks to be invaluable.
There's a canonical document here: http://cs.anu.edu.au/~Robin.Garner/mmtk-guide.pdf. While it appears to be unfinished and very empty, it does helpfully explain the naming convention used throughout the API.
Plans
Plans are ways of bring together collection, allocation, and heap policies into something that can be used by the MMTK. A plan is a package with classes for each of these.
Spaces
A collection of regions of memory, each with a given allocation and collection policy.
Barriers
MMTK currently supports write, but not read barriers.
Policies
A policy is a region of memory with a collection and allocation strategy.
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