If you are a grammar phobic,then please go for http://spellcheckplus.com
This free grammar and spell checker will help you to correct many minor or major grammatical bane. You can either write or paste your content on it.It will simply underline your grammatical loopholes or unspelling.
Unlike expensive grammar softwares,it comes free.
You don't have to shell out a big amount to acquaint yourself with rudiments of grammar.
Its extremely reader friendly.
Its doesnot suffer from any technical flaw.
Its better than spell check offered by windows.
You can also buy its professional edition,which comes around $15.
But,its owner declare that this amount is charged to support this non profit grammar website.
French speakers can may use of its french grammar checker!
Please check it !
Note: It also offers discounts to students and teachers