WS /Samples/PixelStreaming/WebServers/SignallingWebServer/ It's used by SignallingWebServer (based on Node.js web-server) that is part of our PixelStreaming project.We add a dependency to WS library to Node.js configuration and it's downloaded automatically. https://github.com/websockets/ws/blob/HEAD/LICENSE Licensees Git P4 //depot/UE4/Engine/Source/ThirdParty/Licenses/WS_License.txt