Review on ESP-01 Wireless Transceiver Board 3.3V - 📡 4Pcs ESP8266 Serial WiFi Module for Arduino (Updated) by Johnny Black

These things work very well, especially considering their size. You use a serial port to connect to your Arduino or whatever and use an extended set of AT commands to set it up, connect to WiFi and send/receive data. They also support AP mode, making them ideal for configuring WiFi settings by first connecting your laptop/phone/etc. connect to your project's own WiFi connection. If you're using this with the Arduino IDE, there's a great library available on GitHub - search ITEADLIB_Arduino_WeeESP8266. This isn't practical for a breadboard, but it's an easy fix if you buy an adapter, make one, or use Dupont wires.