Pharo does not GC objects with circular references in some circumstances:
miniblog.
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I think Discourse beats mailing lists in many circumstances. It's not yet well suited for sharing patches, but I'm hopeful for the future.
Pragmatic reasons why you can't (in all circumstances) just add floats to a language and simulate integers:
Python 3.3 may change the iteration order of dicts in some circumstances: http://t.co/KAsQX3yX -- it was bound to happen eventually.