Google App Engine hosted application that supports NLTK queries.
For the purpose of testing NLTK, a given text is presented as input and a dictionary is returned as output. The dictionary has nouns as keys and frequencies of appearing in the text as values. The dictionary could be "sorted" using the sorted() function, so that the nouns appear in a descending order by frequency value.
The frequency distribution is calculated for all the tags that have the 'NN' prefix, which means that for a given text, all the nouns will be extracted. In order to refine the text analysis, one could use specific tags, like 'NN$' or 'NN-TL'. For more information on lexical analysis and tags, consult the NLTK documentation.
Another example of refining the result is the use of a blacklist. The current blacklist, when used, gives (almost) only nouns that could be represented graphically, in a drawing or picture.
A running project can be found at nounfreq.appspot.com. Just do a HTTP POST, allowed parameters are:
text the text that needs to be analyzed, which must obviously be URL-encoded.
resultsLimit the number of results obtained for each tag. For the number 2, each tag will give back the 2 most frequent nouns found in the tag's category.