ESP8266-DevKitS is Espressifs flashing board designed specifically for ESP8266 WROOM series modules. It can be used to flash an ESP8266 WROOM module without soldering the module to the power supply and signal lines. With a module mounted, ESP8266-DevKitS can also be used as a mini development board like ESP8266-DevKitC.
ESP8266-DevKitS supports the following ESP8266 modules:

ESP-WROOM-02

ESP-WROOM-02D

ESP-WROOM-02U

ESP8266-DevKitS Board Overview

ESP8266-DevKitS Board Dimensions

Resources
User Guide