Grammar and spell checker
A checker is a type of software that allows its user to automatically detect misspelled words, and sometimes ungrammatical phrases too.
Spell Checker
Spell checking can be considered as the basis of checking softwares. Spell checking capabilities can be found among other things as an add-on for Firefox or within an email service such as Gmail.
Grammar Chercker
Creating a grammar checker is much more complex than creating a spell checker. Not only does it require a word list like a spell checker does, but it also requires those words to be tagged properly and a set of grammar rules to describe the way words should be placed in a sentence. A common with spell checkers is noise, when a correct sentence. That is when a grammar checker sees mistakes where there is no mistakes or when a "mistake" is admitted but settings do not allow to personalize preferences accordingly. A common example of noise is when Microsoft Word French grammar checker detects "nous nous" as a mistake. "Nous nous sommes lavés" is a perfectly grammatical sentence which would translate as "we washed ourselves".