The Nik Collection of 8 programs has been around for some years. Although some of their functionality has been incorporated into programs such as Lightroom, they do have a unique power to enhance color photos and to create stunning back & white photos. The great majority of color or B&W photos I post, print, or sell have been edited in Color Efex or Silver Efex.
The suite of programs is available at https://nikcollection.dxo.com
Kate Silvia has some excellent videos on Nik (and other programs):
https://www.youtube.com/channel/UCCyEw4USV4ho16g58jbwQYg/videos
https://www.katesilviaphotography.com/
https://www.katesilviaphotography.com/video-education
See also tutorials by Robin Whalley:
