Tajima DST is a file format that stores embroidery designs and is used by Tajima embroidery machines. Mac OS X doesn't provide you with a default utility for opening and inspecting this type of files. For this reason, programs like DST Viewer were created.
The application supports drag-and-drop actions and provides you with detailed information about the loaded DST files. After you import your Tajima DST files, the utility enables you to zoom in or out the image, reveal it in the Finder program or send it to the Trash tool.
Furthermore, the app provides you with a quick way to open the imported files in a Tajima DST editor that's being installed on your Mac. You can find the correspondent button on the program's main toolbar.
The only bad aspect about this tool is that it might take a while to launch and to import Tajima DST files.
To sum things up, I'd say it's worth installing this application on your Mac if you work with Tajima DST files often. The program is very simple to handle, offers you details about your embroidery designs, and comes without a price tag.