Online service for doing textual analysis of documents (sent to and online). Realtime analysis. Offers SDKs, so the REST API is probably in there somewhere. Sentiment analysis (general and domain-specific). Classification and categorization. Entity and concept detection and extraction. Hashtag suggestion.

3 hits/second
1000 hits/day for free

By looking around in here you can tell what the API rails are and how to use them:
https://github.com/AYLIEN/aylien_textapi_python/blob/master/aylienapiclient/textapi.py#L84

extract, classify, concepts, entities, hashtags, language, related, sentiment, summarize, microformats, image-tags, classify/unsupervised (picks the most semantically relevant class label or tag), combined (runs multiple analysis operations in one API call).

headers = {
    'Accept': 'application/json',
    'Content-type': 'application/x-www-form-urlencoded',
    'X-AYLIEN-TextAPI-Application-ID': application ID,
    'X-AYLIEN-TextAPI-Application-Key': application key,
    'User-Agent': "Aylien Text API Python " + aylienapiclient.__version__ (0.6.0 as of right now)
    }