Not on the concept, but on one of the features you listed: "a cap on how many times you open something" is harder than it looks on Android, and it's worth knowing before users start reporting wrong numbers.

If you're counting with UsageStatsManager.queryEvents, ACTIVITY_RESUMED fires more often than a person would call "opening the app". It fires again when you come back from a second activity inside the same app, and on configuration changes — rotation, theme switch, font size — because the activity is recreated. Counting raw resume events overcounts, and worst for exactly the apps people want to limit, since those tend to be multi-activity.

What holds up better is tracking foreground package transitions: only count when the newly resumed package differs from the previously resumed one, and debounce a few seconds so bouncing out to a notification and straight back doesn't register as a second open.

The other thing, if you haven't hit it yet: there is no supported way for a third-party app to actually block another app. Digital Wellbeing uses privileged APIs that aren't available to us. Everything else ends up on an AccessibilityService or a draw-over overlay, and both carry real costs — accessibility use is restricted on the Play Store and needs justification, and polling the foreground app aggressively shows up in battery stats, which is its own kind of uninstall.

or, for people who aren't into findom, theres Defang

That's very original: https://www.accountablo.com/blog/apps-that-charge-you-money

And there are a lot more. Also slop.