Clef du Vin wine ager
Search Clef du Vin and you will find another thread. There is no clear explanation of what it does, and strong disagreement whether it "works" or not. [Edit: It appears that the heated discussion was pulled down by the Mods; too bad, there was some good information there].
I have one, have used it quite a bit, and think it works well with some wines. But I cannot explain the chemical/organoleptic mechanism(s).