SysTick and the Core Peripherals
Almost everything on a microcontroller is the vendor's. The timers, the UARTs, the clock tree, the GPIO blocks — all of it is ST's design, at ST's addresses, described in ST's reference manual, and none of it transfers to a part from a different vendor. A handful of peripherals are not like that. They are Arm's, they are built into the processor itself, they sit at the same addresses on every Cortex-M ever made, and code that uses them ports between vendors without changes.