[jrockway]

This is a great example; it almost works like UNIX pipes except that each application has to take an explicit action to share its result with the next application in the pipeline. But like UNIX apps that do something anti-social like rewrite the input file (hello, GNU Recode), that can be worked around.

For those of you that don't use Android, the process works like this. You take a picture. The camera app provides a "share" button. You click "share". Then you're presented with a list of all applications that handle photos. So you can share to G+, or email a photo, or run it through filters, or whatever. The camera application never needs to know about the filter application (the reverse is also true). This makes it very easy to reuse code and for users to design their own workflows. Platforms don't really like this, since they don't have total control over the user experience, but for us users, it's pretty darn nice.

(You can also register URL handlers, so that something like clicking a link to Google Maps in your email automatically opens up the Google Maps app to the same state. Again, pretty useful.)