I found the documentation and firmware for this joystick adapter on the website http://www.hexagons.de/index.php/USB_Joystickadapter some time ago. This is no longer available online for a long time.
It is a joystick adapter with 2 ports for the known DB9 connectors, as they are used with the Atari, or Commodore joysticks.
This adapter can be connected to a PC or the well known MiSTer FPGA hardware, and so the old homecomputer joysticks can be used on modern hardware.