Mac OS X Installer application
The Installer application is always included with the Mac OS X operating system. It allows those who write new software to rely on having a program to install their software on your computer. However, many people who write software for Mac OS X prefer to provide a drag and drop install, so that you don't need to go through an installation process.
The Installer program is used primarily for programs that will put files in several places on your hard disk, rather than just within the "Applications" folder.
Installer packages that Apple approves can also be installed through the Mac OS X Software Update.
It is relatively easy to create your own installer packages, as well. The tools to create packages are free as part of the Apple Xcode Developer Tools suite. You can obtain the Developer Tools from the Apple Developer Connection, which does have a free level of membership.
We are sometimes asked about Optimizing System Performance during software installation; there is an explanation in Apple Knowledgebase article 25807.
