What equipment is needed for APRS?

I'm curious about the hardware requirements for APRS. Could you please elaborate on what specific equipment is necessary to set up and maintain an APRS system? Are there any minimum specifications that must be met? Additionally, are there any optional accessories or enhancements that could improve the functionality of an APRS installation? It would be greatly appreciated if you could provide a detailed breakdown of the necessary equipment and any potential recommendations for optimizing the system.