NB! For OSX there are two files - the final one does not work with older Csound versions than 6.09 well (due to changes in some libraries) - please use the version built against Csound 6.08 on the same page if you have Csound 6.08 or older! (But it has one bug - if there is no CsoundQt config file before, it crashes... )
NB! The Windows version is a zip file - unpack it and run the CsoundQt-d-cs6.exe from there. DON'T OVERWERITE CsoundQt of your previous installation! It is built with msys2/mingw64 compiler and it conflicts with "official" installation if you mix them.
And of course - Csound must be installed previously.