DoubleCommand for Mac overhauls the modifier keys on your machine to match your preferences. This free utility comes in the form of a preference pane and suffers from a very bad layout that makes it hard to use. Despite the design flaws, however, the software does its job well.
Following an installation wizard that requires administrative access, DoubleCommand for Mac creates a new pane in System Preferences, though it adds no new app icon. The window is laid out in a thoughtless manner that doesn't make the purpose of its buttons apparent. Moreover, you'll notice four barely legible number fields, which update as new settings are saved -- clearly a feedback feature used during testing that has no place in the final version. The software supports three ways to save your settings: system-wide, for the current user, and instantly. In addition to the expected tweaks like switching the places of the Command and Option buttons, the utility also allows for the disabling of keys, as well as introducing Windows-style modifier keys like Home and End.
If you come from a Windows background and can't get used to the Mac keyboard, DoubleCommand for Mac will help you reassign the modifier keys to match your old layout. It will also be useful if you actively use both operating systems and want to build some muscle memory. However, due to the poor interface design, this utility takes some getting used to.