The Windows Installer XML toolset (WiX) is a free, open-source toolset that builds Windows Installer (MSI) packages from an XML document. It supports a command-line environment that developers may integrate into their build processes to build MSI and MSM setup packages. This software is released by Microsoft under an open-source license called Common Public License.
On April 5, 2004, WiX was the first Microsoft project to be released under an externally created Open Source licence, the Common Public License. It was also the first Microsoft Shared Source project to be hosted externally on SourceForge.
Rob Mensching, the original author and lead developer of WiX, works on WiX in his spare time. You can read an introduction here: A live one hour Windows Installer XML introduction by Rob Mensching. As of 2006, several other Microsoft employees from various product divisions of the company work on WiX with Mensching, meeting after business hours once a week to co-ordinate development efforts and write code. WiX has proven to be so popular with Microsoft development teams that most of Microsoft’s software products are either already packaged using WiX (as is the case with SQL Server 2005), or will be for their next version (eg. Office 2007).
In a nutshell, to create MSI packages, you just need to create WiX XML files, and then simply run a few WiX tools to compile them to MSIs.
Benefits are: