Cobalt – lightweight HTML5 application container from YouTube

Yeah, looks like there’s no input or img tags. Very limited!

I suspect that list isn't exhaustive. Searching the Cobalt repo shows support for more tags, including <img>. It also supports an on-screen keyboard (likely the platform-specific implementation) as well as game controllers and tilt sensors, so there is support for collecting user input.

It is certainly meant to be a constrained platform for apps. Think of it as a subset of electron, intended for "six foot views" (i.e. television).

In a few words, Cobalt is a de-bloated Chromium designed to run YouTube TV. It's smaller and faster than launching it in the platform's browser.

If you have a smart TV/set-top box/streaming stick/etc bought in the past few years, the YouTube app is most likely running inside Cobalt. You can develop HTML5 applications that can run in Cobalt, but it supports only a subset of html/css/js stuff you'd expect from a browser.