LaTeXiT is a small utility that allows you to quickly typeset LaTeX equations, without bothering with file creation, preambles, and so on. The PDF image obtained can then be exported by drag'n drop to any application supporting it. This is very useful to insert equations in presentations made with Keynote or Powerpoint. LaTeXiT also features an application service, so that you can type and transform equations directly in most text editors (Pages, Nisus Writer Express, TextEdit...).
LaTeXiT is compatible with the most popular versions of OS X. It can be deployed on almost any machine, even the "old" machines in laboratories that will still be used for years. This is not a sacrifice, the LaTeXiT code is optimized: most recent APIs are used if available, and old ones are used if not.