Web Intents is designed to enable web apps to talk to each other, share files and data, without them having to have prior knowledge about other app. It's a proposed standard that should revolutionize the way apps, of any kind, work with each other across platforms and devices.
Pushed by Google and with Mozilla working on it as well, the proposed standard is coming along, though there's still a lot of work to be done.
The feature is enabled by default in Chrome and there are some test web intents apps in the Web Store.
With a recent update to the dev channel Chrome, web intents have passed another milestone, they now work from any website.
Put another way, any website can make a web intent request and the browser will reply with a connection to any installed apps that have registered to be able to perform the actions requested, if any.
This feature is behind a flag for now, so you need to enable it for it to work. Even then, you're going to have a tough time finding sites that use web intents.
A bunch of other web intents fixes and improvements have landed in the latest Chrome builds, especially for Macs, so maybe Google is getting ready for a wider release.
When the technology reaches the level of polish it needs, app makers will start taking notice. Web intents make it possible for apps to work together in ways that require the use of a lot of custom APIs and code today if it's possible at all.
Having cloud storage services be able to send your photos to any photo sharing or editing app you prefer, enabling you to modify them and then send them back, is just one of the many possibilities web intents opens up.