Just wondering because there are nearly infinite possibilities.
Everything allowed from advanced pcb builds over diy brews to simplistic solutions which for example only extend the function of a commercial product via esphome.
I will start right away: Here is the back of a former wall switch which was turned into a smart button with buzzer 
! Total costs were around $2 for the esp12f module+pcb, buzzer and some cables:
My best project that is currently in use is a freezer alarm using a Wemos D1 Mini and a DS18B20 sensor.
An ongoing project is to move my glucose monitors to ESPHome. They are currently running an Arduino sketch on Wemos D1 Minis and communicating over MQTT. My roadblock is sending data to the 14-segment LED displays.
I also have some net monitors around the house that ping my servers every few seconds as well as an external website (at random). I want to move it to ESPHome but there is no way to ping from ESPHome. I can ping from Home Assistant, but depending on HA for the pings would defeat the feature of ESPHome devices being able to run stand-alone.
A custom component for that function exists but it has it’s hard limits (e.g. allows only one target).
Do note that there is a similar flow on discord ‘show off’ and this has pretty funky stuff
ESPHome (discord.com)
I couldn’t find it.
I just created my “Homebrains” pcb where ESP32 controls all my ac relays, led dimmers etc. There is optos in inputs with normal push switch at the wall and small relays after esp. Those will control real 24v/230v 16A relays.
I’ll hook up led dimmers etc to that and all is handle inside ESP32. And of course connection to HA via esp home. Main logic will be inside esp so if HA is down this will work still. Only automations and remote is via HA.
All is made with modules so it’s easy to swap or change if needed.
32 inputs and 32 outputs. 24v system.
WISH ME LUCK 
Good luck! I’m interested to see how it turns out. I have a similar setup (24v push buttons, relays & dimmers) and I was playing with the same idea.
For me its the instantaneous ability to automate anything. My wife bought me a new vacuum sealer that does everything. So I was playing with it, and i marinated some chicken breasts and sealed them up overnight. I had no idea what i was going to do with them. Next day I walk in from work a little early and think. These would be great if i just sous vide the chicken the make a stir fry or something with them once theyre ready. I dont own a sous vide… At least i didnt think I did. I walked into the kitchen, pulled out the slow cooker, filled it with water and stuck one of my weber igrill probes into the pot. hung the bag of chicken breasts over the side. Stuck a smart plug on the end of the cord and told homeassitant dont let it go over 160. I went and walked the dog, took out the trash, did some searches on bing for reward points, etc… About an hour and a half later i go into the kitchen and start chopping vegetables. Pull out my perfectly cooked chicken and cube it up to sear in some stir fry. No pid settings, no fuss. just 2 automations. turn the pot on. turn the pot off.
That is a great idea!
The only thing missing is that my sous vide device (a stick) has an impeller that makes sure the water is circulating for even temp. Given the heating/cooling will cause water circulation, it’s probably not that big a deal for small amounts of food. I was thinking an aquarium pump could help there if it could stand the hot water. (I do 58C for medium steak and 67C for thick sausages)
I made a couple of 3 speed (plus light) fan controllers as the normal smart fan controllers available didn’t have a high enough power rating for the fans I bought.
It has it’s own 240Vac to 5Vdc power supply with over-temp and over-voltage protection. It’s running on a Wemos D1 mini.
The relays are wired such that no two speeds can ever be ON at the same time plus there is software interlocking in the ESPhome code.
esphome:
name: games_room_fan
platform: ESP8266
board: d1_mini
wifi:
ssid: !secret wifi_ssid
password: !secret wifi_password
manual_ip:
static_ip: 192.168.0.132
gateway: 192.168.0.1
subnet: 255.255.255.0
api:
logger:
web_server:
# port: 80
ota:
password: !secret ota_password
binary_sensor:
- platform: status
name: "Games Room Fan Status"
sensor:
- platform: wifi_signal
name: "Games Room Fan WiFi Signal"
update_interval: 60s
switch:
- platform: gpio
pin: D5
name: "Games Room Fan Speed 1"
id: speed1
interlock: [speed2, speed3]
- platform: gpio
pin: D6
name: "Games Room Fan Speed 2"
id: speed2
interlock: [speed1, speed3]
- platform: gpio
pin: D7
name: "Games Room Fan Speed 3"
id: speed3
interlock: [speed1, speed2]
output:
- platform: template
id: custom_fan
type: float
write_action:
- if:
condition:
lambda: return ((state == 0));
then:
# action for off
- switch.turn_off: speed1
- switch.turn_off: speed2
- switch.turn_off: speed3
- if:
condition:
lambda: return ((state > 0) && (state < 0.4));
then:
# action for speed 1
- switch.turn_off: speed2
- switch.turn_off: speed3
- switch.turn_on: speed1
- if:
condition:
lambda: return ((state > 0.4) && (state < 0.7));
then:
# action for speed 2
- switch.turn_off: speed1
- switch.turn_off: speed3
- switch.turn_on: speed2
- if:
condition:
lambda: return ((state > 0.7));
then:
# action for speed 3
- switch.turn_off: speed1
- switch.turn_off: speed2
- switch.turn_on: speed3
fan:
- platform: speed
id: gamesroomfan
output: custom_fan
name: "Games Room Fan"
speed_count: 3
Very nice Dave. How does the 0 to 0.7 thing work? is that like a slider in HA.
Cool i just looked it up on esphome.io, looks like you could switch the split phase motor winding to add the direction change for winter or summer mode.
My proofing cupboard - built using ESPHome to run fully standalone or optionally remotely connected to HA. Actually has 2 ESPs with an opto-coupler separating the side running the interface and logic from the one doing the 240V bits.
The 0 to 0.7 stuff is all about picking up the percentages that HA uses for fan control. Unfortunately they took away the old speed settings we used to have in favour of %. So the below 33% (or translated to <0.4) is the LOW setting, above 33% but below 66% is MED and about 66% is HIGH.
I use a custom card in HA to display the fan control like this:
