Simple Example: Arduino+ESP8266+DS18B20
Pop can solar heat collectors.... I built one of these for a science project many decades ago in fifth grade...it was not as nice looking as this one though.
Remote control lawn mower. Genius.
ESP8266 Heating Controller/Thermostat with Blynk interface
GitHub - martin-ger/esp_wifi_repeater: A full functional WiFi Repeater (correctly: a WiFI NAT Router)
Put ESP8266 (ESP-01) to sleep for saving batteries
Example of processing large volume data with esp8266 and SQL
Four axis 3D printed robotic arm.
Learn how to run a web server on the esp8266. Serve pages to multiple clients. And accept commands directly from the web