Toadstool

Toadstool is a self-contained, breadboard-friendly microcontroller platform that accelerates prototyping by eliminating messy jumper wires.

Toadstool is a modular prototyping platform from Crash-Bang Prototyping, built to speed up embedded development. The core board, like the Toadstool Mega328, houses the microcontroller (e.g., Atmel ATmega328P) and support circuitry, plugging directly into a breadboard for a clean setup. It features an on-board voltage regulator with 5V/3.3V selection and an ICSP header for quick programming. The system’s key differentiator is the 'Caps' modular standard: a dedicated header allows rapid connection of peripherals (SPI, I2C, UART) using pre-made modules, drastically cutting down on wiring and setup time.

https://www.tindie.com/products/crash-bang-prototyping/toadstool-mega328-from-crash-bang-prototyping/