Barrel dice are those weird-ass dice you find on that one dusty shelf behind the counter of your game store. Rather than platonic shapes with numbers on each side, it's a prism shape rounded at the ends, with numbers on the long sides. While not particularly popular, they're an excellent option for d4s, since they don't feel like the torture of a thousand hells to step on. Supposedly, they roll more evenly without as much bias and are harder to "throw", but the larger ones have the same problem as d50s. Hell, a barrel d50 would never ever stop rolling.
If you're super poor and can only afford the pencils and paper for your pencil-and-paper RPGs, your can use your pencils as barrel d6s.