MathType 5 for Mac OS X by Design Science, Inc. - (View article)
Apple.com
MathType is designed to make the creation of complex mathematical notation on the computer simple and fast. It works in conjunction with the software you already own, such as word processors, desktop publishing applications, presentation programs or web-authoring software. Insert professional-quality mathematical expressions into your technical documents, tests, slides, books or web pages quickly and easily using the keyboard or mouse. This is the professional version of the Equation Editor included in Microsoft Office, AppleWorks and many other applications. [More]