From what I recall Sparrow was essentially a spin-off from R&D work done at Apple that Apple did not want to incorporate into their mail app... the dev went off

From what I recall Sparrow was essentially a spin-off from R&D work done at Apple that Apple did not want to incorporate into their mail app... the dev went off and partnered with a designer to build a polished product from that work. An acquisition by Apple would be an interesting turnabout. Of course market validation is a great equalizer.