How do you block unwanted sound from entering a building? Thicker walls, thicker windows, or soundproofing insulation might do the trick, but require a lot of mass. Higher-tech noise-absorbing windows might work, but would require replacing the entire window in an existing building.
Sono is a device that attaches to a window and can be calibrated to cancel certain sounds out (car noise), while amplifying others (chirping birds). It's an add-on device, and you need one per window, but it's a clever idea that perhaps could be eventually integrated better into infrastructure. For now, in situations where noise is a health hazard or a quiet environment is critically important, it's an interesting way to filter out what you don’t need.
You can watch a video that illustrates how the Sono works here, on the Dyson Awards website.