I realize there are things out there like this that are much better but with our exponent unit coming up I wanted my students to be able to see what they were typing using the "^" to denote exponential form and I wanted order of operations to be considered with how they were typing it in the preview. In our practice material (here for example) I have it set up to preview as kids type. It can also be copied and pasted into a document if I wanted to use what I have typed for a quiz of some sort instead of using an equation generator that is sometimes hard to format (or is a picture in some cases).
Here is the link to the work in progress.
I've been thinking for future in wanting it to format complex fractions but have run into a limitation with Google Apps Scripts in not allowing the <u> tag in html or for me to specify what sides of a cell to show a border. I have a hard time believing this would cause a security risk for them but they do not seem to allow that at this time.
**An update as of 5/20/15 now includes fractions with exponential and radical expressions if you type sqrt to represent the square root symbol. Formatting and appearance is still based on order of operations.**