Small boardview file in .brd format, only 22.5 KB, named simply LIO, which may refer to an I/O daughterboard but states no brand, model or board number. Given the size, it likely describes a compact secondary PCB rather than a full motherboard. A boardview shows part placement, pins and net connectivity, useful for locating connectors, fuses and test points. Open it in OpenBoardView or a similar program and compare the outline and component labels with the actual board to confirm what it belongs to.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @pepeelectronica. Enginerys does not host this file.
How to open a .brd file
The most common boardview extension. Several unrelated formats share it, which is why one viewer opens a .brd and another refuses it.