Mirror Images: Similarity in Design
elischiff.com
elischiff.com
The fact is that Geometry -- itself a manifestation of Number -- is the Universal guiding principle that is naturally manifested by systems and/or minds that adhere to it. Not a mystery, really.
There is absolutely no resemblance whatsoever. Other than both being icons of course. Same goes for the next two examples.
In all seriousness though, you're going to see a lot of look-alike design. And that's because everyone submits to the orthodoxy of flat design (or so-called material design, which is flat design with distracting animations). Obviously a designer shouldn't make originality a top priority, as my email example illustrates. But if you don't stick out where it counts (logos, app icons, style), you're going to blend in and get lost.
Google's recent photo app icon is more similar to Google's original Picasa[1] app icon, than it is to iOS Photo's app.