Optiboot (an older version) is installed by default on the Arduino Uno and (as of 2018) official Arduino Nano boards. It can be installed on all older mega8, 168 or 328 based Arduinos. As of 2019, ...

D11, D12, D13, and D17 exist in the pin table but are not physically routed on the board. EXT_VCC D22 / P0.13 Controls the 3.3 V regulator. Defaults to HIGH (enabled). Set LOW to cut power for deep ...