Proboard 21J
Proboard 21J circuit boards are Arduino compatible systems based on the Microchip SAMD21microcontroller. The configuration allows breadboard access to all functions of the SAMD21 ARM Cortex processor, and easy interfacing with external devices.
These boards allow your Arduino compatible code to execute much faster than would be possible if using a less capable Arduino Uno, or its clones. 21J system boards also run CircuitPython code, and they have a bright and colorful "individually-addressable RGB color pixel." These color pixels work the same as Adafruit "NeoPixel" equipped circuit boards - except the circuit board for the 21J is laid out in a more compact form factor.
21J systems plug into standard breadboards, and the girth of the pin spacing for the two rows of breadboard pins is the same as the width of a standard integrated circuit chip. This means that when inserted into a breadboard, a 21J does not cover any of the available breadboard connection points. This makes it easier to find connections for other components when doing rapid prototyping, or testing new circuit ideas.
Check out the Proboard 21J Datasheet to see its advantages.