Mixed-signal Cortex-M4 with 22 analog channels
The internal oscillator means it can run without an external crystal for cost-sensitive builds, though the PLL still needs a clean reference if you push the core to 72 MHz.
128 KB Flash — sizing the firmware budget
The 128 KB Flash (128K x 8) is the mid-density option in the STM32F303R line. It is enough for a moderate control-loop stack with a real-time OS, a USB stack, and a CANopen node, but you will hit the ceiling if you try to pack a full GUI framebuffer or an audio-processing pipeline. The sibling STM32F303RCT6 doubles the Flash to 256 KB — that is the part to reach for when the firmware image outgrows 128 KB.
For dual-sourcing resilience, the pin-compatible STM32F303CCT6 (37 I/O, same core and Flash) is a valid second source if your board can tolerate the reduced I/O count.