There's http://www.azulsystems.com/products/vega/processor, which is a CPU with special GC instructions, created by the same company as one of the most sophisticated garbage collectors. Apparently they thought they could speed things up with specialized hardware. Not sure what the performance looks like in practice, but it is interesting that it exists...
Azul had/has some interesting technology. (They're still around but just do software now.) I had some conversations on this topic broadly at a conference I was speaking at a month or so ago which had more hardware/software overlap than is typical. IMO, we're unlikely to come up with anything else in the near-term that delivered the kind of scaling CMOS process technology did. As a result, it's at least possible that we'll see specialized hardware make more sense in a world where "Moore's Law" won't let general purpose x86 chips just hit the same performance level in a couple of years.
