This shield can be used with or without HydraBus board, you can even cut HydraBus specific right side (on the line) to have a tiny ESP-WROOM-32 breakout board.

• This shield can be used on top or bottom of HydraBus board (you just need to solder ESP-WROOM-32 on top or bottom of the shield)
• The HydraBus board is a small (60mm x 37mm) and low cost, multi-tool extensible board with STM32F405 Cortex M4F 32bits MCU @168MHz with a fully open source firmware hydrafw and full online documentation hydrafw wiki
• The ESP-WROOM-32 is a low-power 32-bit 240 MHz dual core MCU Wi- Fi+BLE combo module that highly integrates TCP/IP network stacks, 12- bit ADC and HSPI/SDIO/UART/PWM/I2C/I2S interfaces. See ESP-WROOM-32 link/info, Espressif Products Overview including ESP-WROOM-32 PDF
• Design based on official esp_wroom_32_datasheet_en.pdf (August 8, 2016)
• Available at OSHPark https://oshpark.com/shared_projects/6t5hURXL