WSOP.com is the online arm of the World Series of Poker, owned and operated by Caesars Entertainment. It's licensed and regulated in Nevada, New Jersey, Michigan, and Pennsylvania — and since all four states are linked under the Multi-State Internet Gaming Agreement (MSIGA), players in all of them share one combined player pool, making it the largest interstate-shared real-money poker network in the US.
The site's biggest draw is its direct tie to the live WSOP brand: it's the only regulated US site that hosts official online WSOP bracelet events, plus satellites that send winners to the live WSOP Main Event and other tournaments on the actual live series calendar.
Outside of bracelet season the site runs a fairly standard mix of cash games, Sit & Go's, and a regular tournament schedule, with traffic that holds up better than most single-state competitors precisely because of that four-state shared pool.