Orca is a Windows Installer package editor provided as part of the Windows Installer SDK that was designed to easily provide full access to the database tables that compose a Windows Installer package.

While Orca provides powerful access to all features of the Windows Installer, it is not intended to replace a full-featured package-authoring environment.

Windows Installer enables the efficient installation and configuration of your products and applications. Orca can be used to create and edit Windows Installer databases.

These include installation databases (.msi files), merge modules (.msm files), database patches (.msp files), database transforms (.mst files), validation modules (.cub files), and patch creation (.pcp files.)

Orca provides direct access to the raw database tables and data streams that collectively define the installation logic for an application. For most editing operations, Orca performs little or no error checking and allows modifications to the database that are not logically consistent or are erroneous.

Directly modifying an MSI or MST file using Orca without fully understanding the potential effects and side-effects of a change may result in an MSI or MST file that does not perform correctly.

While Orca allows the modification of all aspects of the package by direct editing or creation of a transform, the installation packages for some products are designed to work only with a specific subset of all possible customizations or only with transforms generated by a product-specific customization tool.

Customizing a package designed in this manner by means of Orca may result in unexpected or erroneous behavior.