At present, the only way to install and run JQuantity is to download the
sources via the zip file(s), then use your Java development environment to
compile and run.
The jquantity package itself (under JQuantity, together with the util package) provides only main methods which are tests for the various classes (and which are undergoing development).
The spreadsheet package (under SampleApps) provides a (toy) spreadsheet application which utilizes the jquantity classes.