Question: During installation, I got a warning that the developer cannot be confirmed?
Answer: callas software is a registered developer at Apple for MacOS. Due to some quite strict security settings starting with MacOS 10.7 only software downloaded from the Mac App Store can be installed directly. Just change the system settings in 'Security and Privacy' to 'Mac App Store and identified developers' before installing a callas software product. You can set it back to 'Mac App Store' after the installation of course.