If you're one of the many individuals who likes to take advantage of the wealth of free software applications, specifically Open Office, this post is for you! Open Office comes with MATH. MATH is the equation editor that lets you slip math equations into your documents rather easily.
Although I'm a MS Office user and use the Math Type equation editor, which I might add is quite superior to MATH, I did find MATH to be an easy tool to use. I've also been told that Math Magic is another good one, but in the interest of time, I've not yet tried it out. If you use a great math editor and want to share it, be sure to add your comments.

Comments
You should also try SSuite Office’s Math expression builder. It is totally free for download.
Here is a link for more information:
http://www.softpedia.com/get/Office-tools/Other-Office-Tools/SSuite-Office-Expression-Builder.shtml