It's just a really great alarm clock app, but with tons of other sleep tracking functionality. I've always had trouble sleeping through my alarms, but I never do with this.
If you run Home Assistant, Sleep as Android can publish events to an MQTT broker so you can create automations based on those events, like "smart_period", "awake", "not_awake", "alarm_alert_smart", etc.
If you have Hue bulbs (and maybe some other now, haven't looked in a while) Sleep as Android can do that too!
I came to say Sleep as Android as well. Been using it since we were submitting bug reports on Google+ (anyone old enough to remember Google+ ? lol) ... absolutely love it.
As a backup option, you can give Google Assistant or a Google Home the following commands: "at 10PM, sleep {lightname}" to dim, or "at 6AM, wake {lightname}" to brighten - both work over the space of a half-hour, and for some odd reason that's not customizable.