Small ZIP archive of 207 KB named Castw. The name is uninformative and gives no version, brand or description, so its exact purpose cannot be stated from the title alone; in collections of repair tools it most likely holds a utility for viewing board layout or CAD files. Open the archive, read any included notes and check which file formats the program accepts before relying on it. Scan executables first and run them in a test environment if their origin is unclear.
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 @boardview_software_download. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.
Built-in OS tools7-Zip