Q: What is a QSU?
A: A QSU is an "unencoded quest file". QSUs contain all the information found in a .qst file, but in a format accessible to developers who wish to create utilities to use or manipulate quest data in any fashion.
Q: Where can I get a QSU?
A: A QSU file is generated from the "Export" item under the "File" menu in ZQuest, the Zelda Classic quest editor. This means that if you cannot open a quest with ZQuest (because you don't have the password or otherwise) then you will not be able to obtain a QSU for the quest.
Q: So what's in a QSU file anyway?
A: Lots of stuff. If you are interested in developing software to use QSU data, you should download the C/C++ file format definitions:
Q: What programs exist that use QSU files?
A: Other than ZQuest itself, which can import QSU files as well as export them, there are the following (list will be updated as needed):