LaTeXiT allows you to quickly typeset LaTeX formulas without having to worry about file creation, preambles and so forth. The PDF image can then be exported to any supported application by drag-and-drop. This allows you to insert equations into Powerpoint or Keynote presentations. LaTeXiT also offers an application service that allows you to type and transform equations in any text editor (Pages, Nisus Writer Express or TextEdit ).
LaTeXiT works with all versions of OS X. It can be installed on any machine, even those that have been around for many years. This is not a sacrifice. The LaTeXiT code has been optimized to use the most recent APIs if they are available and older ones if not.