Focus is the best! Simple yet effective
This is the best app I've found amongst this category - and I've tried most of them on this list.
It blocks apps, and has white list/black list options for websites. There's a hardcore mode (like self control), and a regular mode.
The app's under active development and the developer is very responsive. I am very happy with this app and my search has ended here - highly recommended! (Full trial is available).
It's less scary/more flexible than self control, nicer to look at and use than Stop Procrastinating, and unlike Concentrate doesn't crash every time I use it. Great stuff.
I like Focus for macOS, but it's not compatible with Windows.
Our users have written 3 comments and reviews about Focus, and it has gotten 19 likes