There's these d8s that use numerals for 1-8 and pips for 1-4 repeated twice. With three different sets of symbols (say by adding roman numerals) you could have a d12 that also functions as a d6 and a d4, though I can't say I've seen one. Trying to put 3 sets of symbols on each die face may create readability issues though.

I think there's other dice out there that function as more than one die but I can't find them atm. There's also ones that are basically just a fidget spinner with various segments or sets of fidget spinners for each die, but you don't actually roll those so I'm not counting them.