Pusher it's an easy and reliable platform with nice features based on websocket protocol: flexible pub/sub messaging, live user lists (presence), authentication...
Bitfinex is one of the world's largest and most advanced cryptocurrency trading platform. Users can exchange Bitcoin, Ethereum, Ripple, EOS, Bitcoin Cash, Iota, NEO, Litecoin, Ethereum Classic...
Blockchain WebSocket API allows developers to receive Real-Time notifications about new transactions and blocks.
SignalR is a library for ASP.NET developers that makes developing real-time web functionality using websockets as transport.
Bitstamp is a bitcoin exchange based in Luxembourg. It allows trading between USD currency and bitcoin cryptocurrency.