Powerful Esp32 Board For Development
Products from EspressIf are ideal for low-cost WiFi and Bluetooth enabled robots or IoT devices.   The Esp32 is a small postage stamp sized module with WiFi and Bluetooth as well as serial interfaces combined with a host of other popular hardware interfacing busses.
Besides an onboard 3D Accelerometer/Gyro chip, LSM6DS3,  we squeezed in a Bme280 environmental sensor onto Rev 3 shown!

It has 3 standard servo jacks with servo power to the upper right. There are 2  counter units ideal to use as two QEI encoder ports!

A serial port for programming and an I2C port as well as SPI port and a Io or JTAG debugger port make this a powerful unit.

4 LEDs and a on-board accelerometer/Gyro unit using the LSM6DS3 are handy too.

Eclipse Dev & several threads on FreeRTOS.

An analog jack with ADCs and dual DACs.

GDB debug using openOCD works now where a J-Link debugger plugs into the JTAG jack.
 
The PC board has plenty of silkscreen to show where parts go as well as document pins

Although the jacks are labeled and planned for some very common IO the pins can juse as easily be used for other functions or just IO.

An onboard 3.3V power supply may be powered from the micro USB jack or a 2-pin power jack.

The 0.1" spacing pins are on an overall 0.1" grid to allow for partial loading and proto-board experimentation as well.
    Built In WiFi and Bluetooth Radios Onboard
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The Rev 4 Mark-Toys Esp-32 based Dev board has a pin compatible I2C connector that allows directly soldering in an optional 1.3"  128x64 pixel OLED display off of the I2C bus is shown here.   Also shown is a temperature sensor that uses the onboard ADC to read temperature.

We now have software to drive several other different sized displays including the tiny 0.96" 128x64 and low power unit with a cost on EBay typically of under $3.

For color and larger display needs see the Robotic Subsystems page on this site where a rather nice TFT Color display has been used and driven from the Mark-Toys Esp32 Dev board.
    Built In Connector for Small OLED Display
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The Esp32 has both WiFi as well as Bluetooth units onboard which make the Esp32 ideal for a great many applications requiring external wireless connectivity.

The board can come up as a WiFi access point (AP mode) for example to allow a connection by a phone to then configure the unit and then have the board become a member of the users wifi network.

The ESP SDK also has support to be able to add a Bluetooth GATT server using BLE (Bluetooth low energy) as a server or a client.    A great many devices these days such as the FitBit or many other devices operate as a BLE server and phones such as Android or iPhones can have apps made to control the device.   Mark-Toys has a few such Android Apps for internal use to control our robots or configs other devices we use this Esp32 dev board for at this time.

Development On The Esp32 Board
Here is the Mark-Toys powerful Esp-32 based IoT friendly board.  This board sports WiFi hotspot or client as well as Bluetooth LE and runs today a BLE GATT server that I talk to with my Android Apps for a few of my projects based on this board.

Development can even be done using the Arduino IDE and the 'ESP32 Dev Board' personality!
Developing code on the Mark-Toys Esp32 Dev Board can be done as simply as through the use of the Arduino IDE using the 'ESP32 Dev Board' personality.

To develop more complex applications I use the esp32 SDK setup on my windows PC which can also be setup on a linux pc.

Many of my applications use FreeRTOS that is fully supported by the esp-idf environment.  FreeRTOS allows a multi-threaded environment with semaphores and other embedded OS features that really make this Esp32 environment ROCK (IMHO).  

You can develop fully command line based using the esp-idf environment (the SDK) OR if you wish to take advantage of the full IDE type of setup you may do as I have and setup the command line tools with Eclipse on top.  The use of Eclipse, although a bit involved to configure, allows many nice editing dev features as well as a nice interface to the JTAG debugging available through use of J-LInk debugger and the JTAG port on this dev board.
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Esp32 Dev Board