Welcome. It's an HP-41cx made by Hewlett-Packard, apparently with some sort of cover over it made by Zengrange to keep contaminants out of the keyboard for use in a dirty environment, and label it for a custom application. The four ports at the end do not need to be filled. When the calc was new, they came with nothing but port covers in them. There were loads (like a couple hundred) of modules available to plug in there, most being ROM modules for more functions (many written in assembly language for better performance and greater access to the machine), but also I/O and extended RAM. There are a couple of engineers who are still writing new modules for these, and modern flash-based modules that hold many ROM-module images in one port.