The Nik collection consist of seven desktop plugins that provide a powerful range of photo editing capabilities -- from filter applications that improve color correction, to retouching and creative effects, to image sharpening that brings out all the hidden details, to the ability to make adjustments to the color and tonality of images. One of their most well known and is the Silver Efex Pro, a plugin for converting your photos to black & white.
Starting March 24, 2016, the latest Nik Collection will be freely available to download: Analog Efex Pro, Color Efex Pro, Silver Efex Pro, Viveza, HDR Efex Pro, Sharpener Pro and Dfine.
The Nik collection is available for PC and Mac, and can be incorporated with Photoshop, Lightroom, Aperture, and Photoshop Elements.
You can find the Nik collection at: Google Nik Collection