There’s also an “ESP8266 IoT SDK”, but from a quick glance at the code, this appears to be an SDK for the SOC on the module, not a simple way to connect the module to a microcontroller.

When we first heard about it a few weeks ago, we knew the ESP8266 UART to WiFi module was a special beast ... and a truly affordable IoT sensor platform is created. If you have a few of these ...