Some of my friends swear by the beet stuff. Dunno, tried some beet root capsules for a month, didn't notice any difference. I've eaten a lot of beets, cooked and pickled, and can't say I noticed any differences. But I still buy 'em occasionally because the dollar store occasionally gets good quality beet pickles for a buck.
Same with cherry juice and other stuff touted as great for inflammation, anti-oxidants, etc. Can't feel any difference. And it's expensive for a placebo. I probably get enough anti-oxidants and anti-inflammatories cheaper through eating good food and aspirin or my prescription meds.
There are some non-prescription supplements and substances that do have definitely effects on most people, but opinions differ over whether those effects are beneficial for athletes. I've found GABA helps relieve some muscle spasms, but it also makes me drowsy so I take it only at night when necessary. It feels similar to taking melatonin. It's just an amino acid, chemically related to prescription gabapentin -- which also seems to help some folks but not everyone.
Ditto natural sources for beta ecdysterone. I feel significant differences. Some folks don't. Sports regulatory organizations are considering whether to ban or regulate it but so far haven't taken any action. It ain't as potent as anabolic steroids and you can get it by eating a lot of some types of greens, shellfish (including the shells) and bugs, for folks with eclectic tastes. And because it's from natural sources the potency varies quite a bit from batch to batch, which may be why some folks report good results and others feel no improvements.
Some folks report great results from foods and drinks containing resveratrol. Red wine contains resveratrol. But red wine, and most alcohol, gives me a sinus headache, so any benefit is negated by the alcohol. I could probably just eat red grapes and see if there's any benefit. Instead I just bought some resveratrol supplement because it's cheap. And it may get even cheaper. Turns out the invasive weed kudzu is a rich source of resveratrol, so the entire Southeastern US might have a cash crop on its hands... and growing up every utility pole.