Dice that work like throwing several coins at the same time, but with less hassle.
The edges are about 21 mm long, and opposite points are 30mm apart.
Paint the numbers to make them show up better. I suppose you could also order coloured and deliberately wear the colour down (to white) around the numbers, but I don't think I'll try it.
There are some games around, usually reconstructions of ancient ones, that require a number of coins or similar flat objects to be thrown, and the score for the turn is the number of them which land showing "heads", or whatever symbol or colour the scoring face carries. Throwing any number of physical coins is usually a nuisance in a restricted space and they don't roll very well, which can lead to doubt about the fairness of the toss. These three octahedral dice are cunningly designed to cover the possible outcomes from tossing 1, 2 or 3 coins*. You can tell them apart by the highest numbered face each one carries, and they carry the right count of each lower number, so that the probability of each possible score matches that from so many coins. By throwing two correctly chosen, or all three dice, at the same time, you can cover the scoring pattern of 4, 5 or 6 coins as well as the 1, 2 or 3 which only need one die to be thrown.
In those ancient games, there are often rules such as "if no symbols are uppermost, the score isn't zero, it's.... such-and-such" (often a higher number than there are coins). The same rule will work just as well applied to these dice.
*When I say coin, I mean something where the outcome is 50:50. Some games use die pieces where one surface is flat, the other curved. These probably don't land exactly as often one way up as the other, say 60:40 instead of 50:50, so if you used the octagonal dice for those games, you would be skewing the probabilities somewhat from the original.
UPDATED MODEL 2020-04-24 after I bought a set to try them. One of the figure 2's on the 2d2 was cut too shallow in the design (my mistake) so I have now made it match the others, checked them all, updated the model and offer it for sale.