https://i.imgur.com/pJAGAZT.png
When I built the house I decided that I was looking for a Home Automation system that was going to be:
a) Open source, or open standards
b) Everything can be done entirely locally
I settled with using the KNX system for the primary actuators for the house, with Home Assistant for automation and control.
One nice property of KNX is that it's distributed, you don't need any central manager for the system to work, so if you press a light switch, then that sends a packet on the KNX network directly to the light actuator. Then there is an IP/KNX bridge to allow you to interact with the KNX network to hack on it.
All the "light" automation in the house is all done using KNX programming. For example, walk into hall, light turns on. You don't need a central authority for that. The motion sensor just talks to the light directly.
For anything more complex, Home Assistant get's involved for all the more "global" automation via the IP/KNX bridge.
And of course you can control everything through it's app. I love how fast and responsive it is since it's local. It's maybe 100ms at most from clicking the button in the app to the light being on.
The main thing I can't do without the cloud is voice control. I'm using Google Homes for it which Home Assistant exposes all my devices to. Local voice control systems really suck compared to Google unfortunately.
Another thing I'm happy I did is just put sensors for everything everywhere through the house. Here is a screenshot of most of them.
https://i.imgur.com/5VeMuE1.png
I actually have more data then this that I haven't bothered to hook up yet since it hasn't been important. Like the motion sensors also provide light levels and so on.
Overall, I would definately recommend Home Assistant.