Your editor has spelling and grammar checkers. Your math editor should check your math. (Not just arithmetic, but algebra, calculus, and proofs as well.) That is what Lurch does; it is a simple math editor with a general-purpose math checker built in.
I am coauthor of Lurch along with Nathan Carter of Bentley University. We were supported by a grant from the National Science Foundation from Summer 2008-Summer 2011 (grant #0736644), and continue to work on the project.
I have integrated Lurch with my course materials and lecture notes in my introduction to proof course at the University of Scranton. You can try it yourself and see Lurch in action at my Math 299 course home page.
For more information, or to get involved, you can read all about Lurch at our github site.
If you have any questions about Lurch, please contact us.