[Slartie]

Which offerings? Are there any?

I only know about other proprietary non-MS solutions like InstallShield, which also generate .msi files but use their own proprietary way to define the installation process, with the benefit/disadvantage (depending on what you want to do specifically) of being on a higher abstraction level than WiX, which is more or less a direct resemblance of the internal Windows Installer data structures.