A boardview (component placement) file. Shared as “Tokyo2 Siv.CST” — a .cst file, 1.53 MB.
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 @ShareMan_Electronic_Files. Enginerys does not host this file.
How to open a .cst file
Text boardview from the Castw tool chain, typical for older ThinkPad boards.
OpenBoardViewBoardViewer