Gmail, Twitter, Facebook, Yahoo, Instagram, Flickr, Amazon
Are the ones I got.
Actually thought Square's was bootstrap.
The the average user, buttons styles may not mean much if at all, but for those that with a keen eye and pays close attention to minute details and pixels, it's quite telling which button belong to which brand.
Saw #4 and was wondering 'What the fracking frack? Is my Little Pony Friends part of this test?' Then I learned it's Microsoft…
The 'easiest buttons to identify for me was Facebook's and Google's.