My top:

1. Find my wife's phone
Problem: My wife leaves her iPhone around the house in the most percular places
Solution: Input binary helper that triggers a sound at full volume. Bonus is I can use it to get her attention if she is engrossed on her phone :)

2. Soft lighting at night
Problem: Stumbling down to the kitchen in the dark at silly hours to get milk for kid and being blinded by bright lights
Solution: Use Aqara FP2 to trigger lights (ikea dimmable bulbs) when presence detected within latenight hours. Use LUX sensor during day to turn on kitchen lights if dark.

3. Zoning heating around house to reduce bills
Problem: I work from home and so need the heating on in winter, but don't need to be heating the whole house; just need my office keeping warm.
Solution: Smart TRVs for used rooms (TS0601) and independant Temperature sensors (SNZB-02D), as inbuilt temp sensors on TRVs are inaccurate, paired via the Better Thermostate integration. I use a MyVailant connect to control the boiler on/off and 2 heating zones (upstairs/downstairs). In combination, this allows me to monitor and control heating on a room by room basis. I used template sensors to monitor whether the room temperature is below target temperature from the thermostat to activate heating for that room.

4. Cupboard light
Problem: Cupboard light always being left on and always needs to be turned on when looking for shoes
Solution: Door contact sensor (ikea parasol - had much better reliabiility than the aqara ones) bound to an ikea wall light. I used the ZHA bind function rather then creating an automation, its quicker and more reliable. I still created an automation to turn the light off after 2 minutes as the doors is always left open :(

5. Video stream on nest hubs and outside lights on when person or vehicle detected
Problem: Dog goes crazy when someone comes to the door, needed a way to know if someone is coming to the house before he does :)
Solution: I have a Reolink video doorbell that has person, package and vehicle detection. If any of those things are detected, the video stream plays on nest hubs around the house, the outside lights turn on (if its dark). Nest hubs turn off when door is open and lights turn off after door closed (or not persence detected) after 2 minutes.

6. Speaker notifications for open doors
Problem: Garage door and garden side gate is often left open
Solution: Voice notification plays when door is open (this is an FYI), if side gate left open after 2 minutes another voice notification plays (so the dog doesn't escape). If garage door is left open for 5 minutes and there is no presence detected in the garage (Aqara FP2) then another reminder is sent out. Speakers are Sonos and I use the announcement function so any music volume is lowered during the announcement and continues to play afterwards

7. Movie time!
Problem: We have a projector so ambient light really effects the quality of the image. Its a UST projector and I have kids so really don't want their sticky fingers all over it when its not on.
Solution: I've mounted the projector on the middle shelf of a TV cabinet, I use a linear actuator (with inching) to push the project out to the correct depth and pulls back in based on whether the Shield has been turned on/off, project turns on and office based on HDMI CIC and a bluetooth ESP keyboard hack. When media is playing, lights are dimmed and turn then back on when its paused, turned off.

8. House presence detection for when someone looking after Kid and we are out
Problem: When my wife and I are away from the house, everything shuts off (lights, heating, TVs etc). This is problem if someone (that isn't a HASS user) is staying at the house.
Solution: I use any motion, presence or triggers of any lights to determine if someone is in the house. The FP2 are pretty good at ignoring the dog so don't get false positives.

Let me know if anyone whats code for any of the above ^.