Windows Installer XML (WiX) toolset has released as Open Source on SourceForge.net. This is the first Microsoft released product to be under an Open Source License. Bascially its a set of tools for creating MSI Installers using XML. There is a complier called Candle, a linker called Light, a lib tool called Lit, and a decompiler called Dark (cute huh?). Anyway, here is the link on Rob Menshing's Blog about it, and here is the project link on SourceForge. Looks very promising.