I'm using some ESP8266 "D1 mini" modules, mostly for retrocomputing :)
Thats how I got into using the ESP8266.
I've built one that acts as a WiFi modem, it uses the "esp_modem"
firmware that I've changed slightly to fit my needs. It emulates a
modem (so it understands AT commands) and is connected to one of my RC2014 Z80 computers running CP/M and a terminal program.
Another nice option is the "ESPterm" firmware, it acts as a terminal: It
features a webserver that you can connect to via a webbrowser. On this webpage, you then see a "terminal window" that is talking via the serial
port of the ESP8266 to the attached machine, eg. a Z80 CP/M computer :)
Both are wicked cool... I did somewhat the same, and from there I started playing with ESP32s.
I use them for Home Automation...
|07p|15AULIE|1142|07o
|08.........
--- Mystic BBS v1.12 A47 2020/11/23 (Raspberry Pi/32)
* Origin: 2o fOr beeRS bbs>>>20ForBeers.com:1337 (1337:3/129)