Written by a Microsoft MVP to create or update MSI (Windows Installer) based installers for files, registry etc using an XML like script. Has command line support for use in unattended builds (NMAKE, ANT, NANT builds etc). It builds a HTML report by default (with a "file verify" button). For both beginners and advanced users. Common processes can be defined once and reused in multiple projects (templates). Has extensive documentation and a large user group (500+ members). A MSI compare or disassemble tool is available which generates MAKEMSI output, this is commonly used by people wishing to automate tasks they currently use ORCA for.
Also has a framework for easy MSM (merge module) and CUB (MSI validation suite) building.