All of Microchip ’s baseline PIC microcontrollers have internal 4-MHz oscillators, which are useful for freeing up one or two pins for I/O use and allowing you to build minimal-component-count designs ...

This allows it to be used by developers more familiar with non-functional programming languages. OCaPIC is a compact OCaml implementation that runs on an 8-bit PIC18 microcontroller from Microchip.