Natural Language Processing Package
nlp, stanford-nlp
Solution
You didn't really give much info, but try this: http://www.nltk.org/
I don't think NLTK does spell checking (I could be wrong on this), but it can do parts of speech tagging for text input.
For finding/matching synonyms you could use something like WordNet http://wordnet.princeton.edu/
If you're doing something really domain specific: I would recommend coming up with your own ontology for domain specific terms.
Problem
I have started working on a project which requires Natural Language Processing. We have do the spell checking as well as mapping sentences to phrases and their synonyms. I first thought of using GATE but i am confused on what to use? I found an interesting post here which got me even more confused. http://lordpimpington.com/codespeaks/drupal-5.1/?q=node/5 Please help me decide on what suits my purpose the best. I am working a web application which will us this NLP tool as a service.