Excellent replacement for Isolator
I’ve been using Isolator up until now, but it has some issues with full screen apps on El Capitan, as well as some other niggling little problems that I usually just work around. It’s basically unmaintainted, so I did some Googling for alternatives. One page I found recommended HazeOver, and it Just Works™. No workarounds required. Good stuff.
There’s also a demo version on the home page, if you’re not sure whether it’s for you.
Kestwool about HazeOver • Distraction Dimmer™