WebRTC is a free, open project that provides browsers and mobile applications with Real-Time Communications (RTC) capabilities via simple APIs. The WebRTC components have been optimized to best serve this purpose.
Agora video voice allows you add implements real-time high quality video chat into any application. Agora video voice includes all the development tools and cloud infrastructure needed for mobile, web, and desktop applications.
The OpenTok iOSSDK lets you use OpenTok-powered video sessions in apps you build for iPad, iPhone, and iPod touch devices. The best way to learn how to use the OpenTok iOSSDK is to follow the OpenTok Basic Video Chat tutorial: via its parent site.