Java has an excellent GC, but a horrible runtime. .net is probably the best GC integrated into a language with decent memory layout ability. If all you want is the GC without a language attached, LXR is probably the most interesting. it's part of MMTK which is a rust library for memory allocation and GC that Java, Ruby, and Julia are all in the process of adding options for.

LXR isn't that great when the amount of heap memory is actually reasonable rather than being unnecessarily low. Watch the ISMM talk I linked above.

ZGC