Of apps, I am currently using ScreenZen, which links into ScreenTime to provide a warning message and delay before I browse a customisable list of websites/apps. (HN is on it...) It seems to work better than OneSec, though it isn't perfect.
[update] Another thing I find useful is to regularly measure my screen time, and have a manageable goal for how long I spend. That's more productive than hoping to go "off-grid" forever.