.ust files?

So, I was looking at vocaloid sheet music the other day, but I noticed that a bunch of them came with these .ust files. I have no idea what they are, and when I tried to google them, it lists it as a "a WiFi SiStr exported user theme", which... is not really applicable XD

Does anyone know what these are and what program can read it? My computer certainly doesn't know.

UST files are files especifically made for UTAU to read, they contain the voice data, the notes and everything needed for an UTAUloid to sing a certain song, like if you have a Romeo and Cinderella UST you can import it to UTAU and have it sing the song, with any voicebank you desire, I download a lot of those because I use them for my UTAU XD so yeah, they are files for UTAU

Thank you so much for your help! I downloaded something and it appeared on there... just now how I can make it useful XD