I can name two platforms where the recent Bitcointalk Poker Series were played.

One of them is Betnomi, which I personally enjoyed very much, but I must say that some people were complaining about occasional log outs during the game. It was always taking me less than 15 seconds to be back in, so I didn't see a problem there.

Another one is SwCPoker, a smooth and established platform where our gang from Bitcointalk played many tournaments, and we enjoyed it very much.

Also, in 2020, Sportsbet.io were setting up several tournaments with good money added to the prize pool by the owners. They had stopped poker completely on their site since, I believe, last Summer, with the intention of getting some better poker software and come back this year, so, it might be a third option.