Metz is a German consumer electronics manufacturer. The company was founded in 1938. One of its best known product lines is a set of flash units branded Mecablitz.
The flash guns with the AF designation are dedicated shoe mount flashes that are built to work with a single, dedicated flash system. The flash guns with the MZ and CL designations are based upon Metz' SCA (Special Camera Adaption) system. SCA is modular, and let you tie a flash to a particular dedicated system with a suitable adaptor (typical cost USD 80 per adaptor). You may move a flash to a different system by buying the right adaptor for that system.
Some Metz flash guns have a USB-interface to let users upgrade the firmware for newer camera models.
Metz flash guns has an excellent reputation for performance and build quality, but they also carry a high price tag.