I hate the way it looks and it has no charm, but...
3M abrasive tape.
I've tried other things, but they didn't hold up and folks still slipped. What is the cost of a bad fall for a family member
? Far too high for me. And your answer when a guest slips and says the step was too slippery is "I don't like the way 3M tape looks?"
You would think it would be hard on bare feet, but it isn't and it is far easier than jammed toes from slips.
But it has no charm. Each boat I have put it off for years, and eventually gave in a few troublesome places.