EzMath is an editor for mathematical expressions. It uses a markup language of its own which is easy to read, and it can also export content MathML (See MathMl).
There is also a plug-in to display algebra in, e.g., NetscapeNavigator.
For details see http://www.w3.org/People/Raggett/EzMath/
-- JohnFletcher
See also MathWiki