Lots of things. The original design for this chip was to have a serial to WiFi bridge. I use one of these as exactly that: a WiFi connected serial console for one of my home servers so I can get into it even if for some reason it isn’t on the network.
But you can also do so much more: these chips have lots of GPIO pins so you could control anything that an Arduino or another microcontroller can control such as relays, displays, temperature/humidity/proximity/etc. sensors, LED strips, motors, heaters, and so on. But the kicker is that with built in WiFi so you can natively get it online. A lot of smart lights now have these chips in them for example and you could make your own. Or your own internet connected green house with vents you can open/close and sensor readings for temperature and humidity in the air and the soil. Or an RC car you control from your phone. Or shades that open and close based on time of day. Or a garage door opener. Basically if you need a gadget you control over a network, these probably should be your first potential solution. They are low power and physically small compared to something like Raspberry Pi’s or other single board computers and more powerful than Arduinos.
Given all the air quality issues in CA right now, I've been planning to put together an air quality + temp + humidity sensor that I can run off a battery and connect to my wifi. I already bought the sensors which I have connected to a Raspberry Pi just to play around with them, but of course a RPi won't last long on a battery. I really want something I can just toss in the corner of a room and easily move around.
I've mostly been looking at the ESP32, though (newer, also has bluetooth and 2 cores, and is lower power), and some of the ARM Cortex-M-based microcontrollers.
As the device has onboard WiFi I can poll a remote site to get data and display it, updating every few minutes. I use that to show the next departure-times at the tram-stop round the corner from my house.
Sure I could use an app, or even walk there and wait, but it's nice to know when to leave - especially in winter-time!
Get an Arduino starter kit and start hacking on some little project around the house. With a bit of persistence, C/C++ is not so difficult to become productive coming from almost any other language. And with the help of platformio's [1] CLI tooling it makes uploading and debugging your code on chips like the ESP8266 (or ESP32 or Arduino) pretty straight forward. Then of course there are the actual physical pieces of hardware, wires, circuits, components, etc. It's a whole new world in which to learn and break stuff. Good luck!
So much this.
You can tie in to Home Assistant quite easily. You can then make all sorts of things. Buttons to turn things on, screens to show data from Home Assistant, measure things (distance, door open/closed state, humidity, light/dark, weight etc). The sensors are nearly all really inexpensive and seem to be pretty accurate. From knowing nothing to having something functional working takes a few hours. It’s great fun and anything with lights and sound gets kids involved very easily.
