DST is Tajima's industrial embroidery file format and the most universally-supported design format on commercial machines. 512-byte header followed by 3-byte stitch records. Brother, Janome, Bernina, Singer, Husqvarna Viking, all read DST as a fallback even when their native format is different.
How to open
Every commercial embroidery machine. Free viewers: Embird (paid), Embroidermodder (free), online embroidery viewers like StitchView.