Create or update MSI (Windows Installer) based installers for files, registry etc using an XML like script. Can 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 (450+ 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.