An installation program or installer is a computer program that installs files, such as applications, drivers, or other software, onto a computer. Some installers are specifically made to install the files they contain; other installers are general-purpose and work by reading the contents of the software package to be installed.

The differences between a package management system and an installer are:

A currently popular format for Microsoft Windows is the MSI installation package, which is installed by Windows Installer. Companies making tools for creating installers for Windows include InstallShield, SetupBuilder, Wise, ScriptLogic Corporation (Formerly MaSaI Solutions), InstallAware, BitRock and OnDemand. Most of these tools can create MSI packages as well as their own proprietary executables.

Free alternatives include NSIS and InnoSetup, and a tool from Microsoft called WiX. BitRock has a multiplatform tool, called InstallBuilder, that creates installers for Windows, Mac OS X, Linux and many others and is free for open source projects.

Mac OS X has an application called Installer bundled with it. However, this is not technically an installer (see table above). However, some commercial applications use a custom installer, often Installer VISE or Stuffit InstallerMaker. Applications that do not need to install additional system components can be installed by a simpler route, namely moving the application files from the install disk or download location to the location where the user wants it to be installed; this is known as "drag-and-drop installation" and no installer software is needed. Note that Mac OS X also includes a separate software updating application, Software Update (also known by its shell command, "softwareupdate"). However, this does not support third party software and works only on system software.

An installation program on a CD is often designed to run automatically when inserted into the optical disc drive.

See also

• Installation (computer programs)
• Package management system
• Software distribution
• Uninstaller

Software | Installationsprogramm | Instalator (informatyka) | Installationsprogram