This small board can act as WiFi module for Arduino (or other µc - Teensy, Netduino, etc) or as standalone microcontroller. With RISC processor running at 80 MHz and with 4MB Flash You can do lot interesting projects. It has 9 GPIO pins to interact with other modules (OneWire, I2C, SPI).
ESP8266-12 technical details
9 GPIO ports, each PWM capable
RISC processor 80MHz
power supply 3.3V (3.6V max)
logic levels 3.3V
PCB antenna
4 MB of flasg
To program ESP You will need FTDI friend or USB/Serial converter. FTDI cable 3 V will work only if You provide other power source, FTDI cable, even 3V version has 5V at it's power line.
W also carry adapter, which has all ESP GPIO in 2.54 raster - You can plug this adapter directly into breadboard or connect standard F-M cables.
Power supply During start and in some working modes ESP takes up to 220 mA of current. Not all USB/Serial converters will provide such current. In that case You will need some separate 3.3V source to power module. More on ESP8266 current consumption topic. TL;DR: module takes from 220 mA in 802.11b mode, through 130mA - 150 mA in n or g modes to single mA in power save modes.
What can I do with ESP8266-12?
This module works as WiFi gateway for other µcs, or as standalone node. Check this example (in polish) how we did connect DS18B20 temperature sensor to ESP8266-01, and it's sending data to ThingSpeak: Nettigo::Blog
To program this module You can use LUA language, just upload nodeMCU firmware and You are ready to go :)
Useful links
nodeMCU fw on github
AT commands nurdspace.nl
ESP8266 Wiki
Tool for firmware uploading: ESPLORER
Open project SUPLA - home automation with ESP8266 and other modules