Parodinal is a Rodinal-type developer made from Tylenol and sodium hydroxide as the main ingredients. It seems perfectly interchangeable with Rodinal in terms of developing times, but seems to me to be a little less gritty--maybe more like Rodinal with a little extra sulfite to take the edge off, which has been a historically popular Rodinal modification.

As I said, I just tried it out of curiosity, because I has a bottle of expired Tylenol tablets I was going to throw away anyway, but even if you had to buy fresh generic acetaminophen tablets, it turns out to be significantly cheaper than Rodinal, not that Rodinal is so expensive that I'd worry about it.