This feature isn’t exclusive to the Leonoardo, as [Michael] explains in a build he sent in – the lowly Arduino Uno can also serve ... to have your old Arduino board gain some of the features ...

Allowing an Arduino to become nearly any kind of USB device. A fourth mounting hole has been added to the UNO for more stable mounting. The booloader is now the Optiboot bootloader. The boards can ...

Connector to add external battery to real-time clock (RTC) inside Renesas MCU (MCU RTC power pad held to 5V rail on Minima) Secondary (wireless) processor: 240MHz 3.3V dual core 32bit Espressif ...