From the site: WPKG is an automated software deployment, upgrade and removal program for Windows.
It can be used to push/pull software packages, such as Service Packs, hotfixes, or program installations from a central server (for example, Samba or Active Directory) to a number of workstations.
It can run as a service to install software in the background (silent install), without user interaction.
It can install MSI, InstallShield, PackagefortheWeb, Inno Setup, Nullsoft, other software installers or .exe packages, .bat and .cmd scripts and similar: no more repackaging to perform software installation.
WPKG is open source software.