[frompdx]

Overleaf.com uses websockets for collaborative LaTeX editing. I personally think making a nice git workflow for non-technical academic types who are stuck using LaTeX might have been better.

Slack and probably any other chat app.

A certain hardware vendor for networking equipment uses websockets to tell device's when a user wants to establish a connection to that device. Websockets are used to broker webrtc/p2p connections in that case.