I have an old Nexus7 tablet mounted on the wall (3D printed wall mount which incorporates a wireless charging coil) which hits the web UI of NodeRED running on a Pi to provide a 'home control panel'.
There's a pi with a heap of relays which controls things like my garden lights, sprinklers, motorised curtains (3D printed adapters to convert standard curtain tracks into motorised ones), etc, and then I have a number of Orvibo S20 WiFi power sockets to switch things like lamps on and off.
I have a pi mounted behind the front entrance panel acting as a doorbell, also connected to a camera module which triggers push notifications etc when motion is detected. This also ties back into the main 'automation hub' via NodeRED.
I also built an aquarium monitoring/control system on another Pi, with ambient and water temperature probes, a bunch of relays turning filters, lights, heaters, pumps, etc on and off, and an IR-emitter to send the relevant commands to my lighting fixtures to control the colour temperature and intensity (providing a 'sunrise'/'sunset' effect). Again, this all ties back to the main system using NodeRED.
Unrelated to the home automation, I also use a Pi to manage and run my 3D printer using OctoPrint, and run my media centre using LibreElec/Kodi/Emby (with my media stored on my main workworkstation and served via Emby).