New in latest versions: WebGL build support added.

Supported platforms:
-WebGL
-iOS(+ IL2CPP 64 bit), Android
-Windows Phone 8.0, 8.1, 10, Windows Store Apps, Windows 10
-Webplayer and Samsung Smart TV with some restrictions
-Windows, Mac OS X, Linux

Most notable HTTP features are:
-Customize all parts of your requests:
-+Methods(GET, HEAD, POST, PUT, DELETE, PATCH)
-+Headers
-+Cookies
-+Max redirect count
-+Timeouts
-Access all kind of data sent by the server:
-+Headers
-+Status code
-+Cookies
-Connection pooling
-Connection and request timeouts
-Automatic Cookie handling
-Great range of Proxy support (Fiddler, Charles, etc.)
-Automatic caching, validating just like your browser
-Set your cache size and freshness
-gzip content encoding
-Basic and Digest authentication
-Multiple (url-encoded and multipart/form-data) form types
-Automatic redirection handling
-Upload and Download progress tracking
-Access your data while downloading
-You can resume downloads using Range headers
-HTTPS
-Customize a great range of global settings:
-+Max connection per server
-+Enable/disable cookies
-+Private 'Browsing'
-+Cookie Jar size
-+etc

WebSocket features:
-Full RFC compliance
-Easy to use, 'just works' experience

Socket.IO features:
-Compliance with the latest (1.3.+) Socket.IO implementation
-Automatic transport upgrade/downgrade
-Binary data sending/receiving
-You can plug in your favorite Json decoder

SignalR features:
-Works with the latest SignalR implementation
-Easy to use API
-Hubs
-Support for authentication
-Progress messages for long running jobs
-Automatic transport upgrade/downgrade
-You can plug in your favorite Json decoder

Server-Sent Events features:
-Compatible with the latest specification (http://www.w3.org/TR/eventsource/)
-Easy to use API