The ESP-32-based M5Stick-C is a wee, super portable, open-source IoT development board, like a fun-sized version of the M5Stack.
Jam-packed with a Wi-Fi & Bluetooth powered ESP32, USB interface, Li-Poly battery and charge circuitry, 0.96" color TFT display, various sensors (IR transmitter, microphone, 6-DoF IMU sensor) all integrated inside, buttons, and more! You can plug Grove sensors into one end, or use the 0.1" header sockets on the other, to connect additional sensors or actuators. It's perfect for making ultra-small IoT projects or wearables.
Despite it's small size, its a very capable, all-in-one development board that can be used to build advanced projects with wireless sensing capabilities.
M5Stick-C is one of the core devices in the M5Stack product series. It's compatible with many of the modules and add-ons in that ecosystem, which opens up much potential in the developing IoT landscape (or perhaps we should say...cloudscape?)