MSIDIFF 06.081     
MSIDIFF compares or decompiles Windows Installer Databases (MSI, MSM etc)

PPWIZARD - HTML PREPROCESSOR 06.109     
Free HTML preprocessor - Better than "SSI". Imports from SQL databases.

MAKEMSI 06.119     
Builds or Updates MSI based Installers. Has MSI decompiler/difference tool.