I've always used Blake's Deck Paint without additives. You can add additives to make it extra non-slip but I find it provides enough grip without the grit. It is self chalking so you don't get a build up over the years. Not the most satisfying thing to put on - it's quite thick and so doesn't brush out far.
International/Epiglass also make a dedicated Deck Paint containing a small amount of fine sand, which has to be stirred up from the bottom of the tin. The paint is also a matt finish. I suspect that most of the paint manufacturers make a paint of ths kind.
Peter.
I've not used it myself but have been told that ordiary exterior paint with sugar added leaves a non slip surface when the sugar disolves ! Sounds interesting !