Actually, MathType is a professional math typesetting program. The version that comes with WordPerfect and MS Office 2003 (and earlier) are watered down versions. The full version of MathType can be used to embed equations in any program, including MS Works or Wordpad, via OLE.
It is not a free program however. There are many free GNU alternatives; but like most GNU programs, they tend to lack either features, ease of use, or both. LaTeX is a powerful typesetting language for mathematics, and you can certainly find many LaTeX or MathML editors for free; however, they tend to be quite a bit more difficult to use.