Classical Opus is freeware and it is not to be sold for profit. It is available only for Windows 10, 8, 7, Vista, XP and possibly below.

Classical Opus's latest version can be downloaded either from this home site. No other site is authorized to maintain the latest Classical Opus version.

File : ClassicalOpus.zip
 (Please click on the link above to download file.)
Size : 2.2MB
Content : Classical Opus 4.0.0 program, help file, manual, tutorial, music glossary.
Installation: unzip will create folder CLOPUS. Open folder CLOPUS and run setup.exe

Windows 64-bit UPDATE (Windows 10, 8, 7, Vista, XP 64-bit only) 
If you are installing Classical Opus 4.0.0 on a Win 64-bit system such as Windows 7 64-bit please download and install this update after you install "Classical400.exe" above.

.File    : CLOPUS_500x64_Update.zip (2012 update)
          Please click on the link above to download file)
Size    : 1.5MB 
Content : Classical Opus 64-bit update (installation of Classical400.exe below is required before you apply
          this update). 

Guide   : The CLOPUS_500x64_Update.zip update will update the sorting engine to Classical Opus 5.0.0.
          1. Download and Install from ClassicalOpus.zip from above
          2. Download and unzip CLOPUS_500x64_Update.zip above
          3. From the resulting CLOPUS_500x64 folder, copy all files
             to the "C:\Program Files\Opus400" or C:\Program Files(x86)\Opus400
             directory where you installed Classical Opus 4.0.0
          4. By copying please allow for the replacement of any files within
             "C:\Program Files\Opus400" or C:\Program Files(x86)\Opus400 folder
          5. From now on run the "Classical500x64.exe" or "Classical500x64" file and everything will work
             fine. You will be using Classical Opus 5.0.0 on your 64-bit system.

This is absolutely SAFE software!!!