A group of researchers and engineers working out of Harvard University are developing exceptionally high-tech smart windows that are capable of adjustable opacity, which allows you to control the amount of visibility and privacy offered by the windows.
While smart windows already do exist, they tend to make use of electrochemical reactions in order to be able to alter their transparency and opacity. While this is undeniably effective, it is very expensive and often requires the use of toxic materials. However the Harvard smart window uses a regular glass or plastic sheet that sits between two clear elastomer layers treated with silver nanowires, which can be activated to compress the elastomer layers and distort them, making the windows frosty in appearance.
Seeing as how they're based on physical rather than chemical technology, these smart windows could make tunable windows more affordable for both commercial and private applications.