Minim OSD is a standalone component that allows you to add OSD data to analog video. The OSD chip is included in the vast majority of controllers today, and standalone OSD is more of a thing of the past, but there are cases where it is needed.
You will use the standalone Minim OSD when using a Pixhawk controller in combination with analog video. For more information, see here. The Minim OSD includes an OSD chip (MAX7456 or clone) and a microcontroller ATmega328P that can be programmed via the Arduino IDE. Thus, the minim OSD can be used in DIY projects that work with analog video.