The Network Information API enables web applications to access information about the network connection in use by the device.
Knowing the type and properties of the connection allows applications to make informed decisions about how/if/when it should fetch resources, and/or modify what type of resources are being fetched -- e.g. kick off background sync when on WiFi, fetch lower resolution media when on <3G, and so on.
Brief history... DAP working group worked on the initial draft of this API but then discontinued their work. Since then, we've gathered more use cases and updated the editor's draft to address some of the previous limitations: http://w3c.github.io/netinfo. However, as it stands, the spec doesn't have an "official working group home"...
I'd like to propose that we move it under the WICG umbrella. Thoughts, comments?
p.s. fun fact, Chrome on Android (48+) and ChromeOS both support the functionality in the editors draft, see demo page.