This is the upgradation of ESP-01 board, had small improvement on PCB.
1MB (8Mbit) Flash size.
AP, STA, AP+STA modes available.
Very simple AT commands, easy to use.
Internal LWIP interface.
Only four pins interface, VCC-3V3, GND, TXD and RXD.
AT commands firmware. New IC ESP8266ex
Accrediting to ai-thinker, only add two parts, improve antenna, fully compatible and replaceable for ESP-01