D3DOverrider is a 3rd party application that was installed, but not utilized, with RivaTuner back in the days when overclocking or monitoring GPU was at a primitive state.
You have to install RivaTuner and extract a folder in there that contains it. Just to save the trouble, I'll upload what I am using. Uncompress it, and run D3DOverrider.
Download this
You can force vsync in DirectX games that does not appear to have option for it, or does not allow vsync in certain situation (eg Far Cry 3 does not allow vsync option when playing in windowed mode...).
Of course, the main purpose is Triple Buffering, which helps with reducing sudden fps drops associated with Vsync, and improves performance quite a bit when vsync is turned on.