The Duo looks like a capable development board for IoT designs. The small board uses the same form factor as a few other IoT boards such as the Spark Photon, WiFiMCU and the NodeMCU. It comes with Wi-Fi and Bluetooth that supports Apple HomeKit and uses the Ampak AP6212 module which has a STMicroelectronics STM32F205 120MHz ARM Cortex-M3 with128 KB SRAM and 1MB Flash together with the Broadcom BCM43438 to supply Wi-Fi and Bluetooth connectivity. RedBear also have an RBLink expansion board which works together with the Duo and allows you to plug in a wide range of Grove sensors made by Seeed Studio.

The system is compatible with the Arduino IDE and with the Particle Web IDE, Dev and CLI which allows you to program the Duo online and wirelessly. You can even use the Broadcom WICED SDK for low-level tweaking and an open-source JavaScript interpreter is being ported to the microcontroller.

The developers have partnered with Particle, to give the Duo free (for the lifetime of the Duo) Cloud service.

Key features of the Duo:

• STMicroelectronics STM32F205 ARM Cortex-M3 @120 MHz, 128 KB SRAM and 1 MB Flash
• Broadcom BCM43438 Wi-Fi 802.11n (2.4 GHz only) + Bluetooth 4.1 (Dual Mode) combo chip
• On-board 16 Mbit (2 MB) SPI Flash
• Integrated chip antenna with the option to connect external antenna
• 18 I/O pins
• RGB status LED
• Small single-sided PCB for easy mounting on other PCB boards
• Duo comes with headers soldered
• 20.5 mm x 39 mm

Duo is currently up for funding on Kickstarter and early bird offers for the Duo are priced at $19 but are all gone. You can still secure yourself a Duo with a pledge of $22.