It started as a necessity project and evolved over time. You see my daughter started to wanted to have her independence around 5th grade (11 years old) and didn't liked me or her mother to go to school or get her home from school. So she needed a key to enter the apartment. Problem was that she lacked the necessary strength to actually unlock the door - door lock had a certain key position and until you hit that position it required quite a strength to do that. So every day she came from school she was ringing at the door. Whoever (me most of the time) was at home, had to go to the door and open it for her.
So that's how I started this project. Get the door to be unlocked. Bought a new lock, with electromagnetic locker in it, hooked up a Raspberry Pi to command a switch for 0.5 seconds and then wrote a server application for RPi that does the command. Wrote another Android app, that connects to RPi, sends the user/pwd via WiFi, the server verifies if all is OK and then unlocks the door.
Then started expand the tech. Get new users to be added by an Admin user (so roles were implemented). Used as DB SQLite in RPi. Wrote my own protocol on top of crypto libraries so communication is secured with a 4096 RSA key over WiFi. Then one day a little accident happened - my daughter had problems with her stomach and the door could not open fast enough for her to go to toilet, so a little soiled pants came out of that event :).
That prompted me to start expanding even more and invest in a little LoRa PCB attached to RPi so the communication now can happen from distance instead of just few meters from the door.
Then I wanted to expand the usefulness of RPi. So when we go to vacation a little pump is pumping a predefined liters of water on our flower pots. And to make sure those do not actually get too little or too much I hooked also a number of webcams on RPi to watch them. And since I was at this step and I wanted to flex my muscle in computer vision so another camera is on our front door and automatically will try to recognize people going through its field of vision. This last step is still refined. So this is where I am with this project. Still in development, pretty sure I'll have more ideas in the future I'll attach to that RPi.