Even if I wanted to smartify my home using open source and local servers. I wouldn't even know what to make smart.

Lights only ever need to be on when I am in the room, but every door has a switch that only requires my arm to lift a bit. So what is the point in powering electronics for that? Just wastes energy.

Anything with a lock is a no-go anyway.

I rarely close my curtains, and don't see why they should do so automatically in the off chance of it happening.

I don't need to touch my thermostat when I am not at home.

Can anyone tell me actual useful applications that aren't just a gimmick?