An online bookmark manager which also can act as a content archiver. Can save content as HTML, PDF, or PNG in addition to storing links for later reference. Automatic summarization and tagging of links. Multiple user accounts. Multiple back-end databases (SQLite default). Annotation support. Written in Python 3. Don't know if there's an API.

This source code is an implementation of the TextRank algorithm (Automatic summarization) on PHP7 strict mode. It can summarize a text, article for example to a short paragraph. Before it would start the summarizing it removes the junk words what are defined in the Stopwords namespace. It is possible to extend it with another languages.

An online collection of 101 level tours of programming languages. If you have to get up to speed in a hurry, you might find something useful in here. Has overviews of common tools, also!

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)
    }

Python module that implements the summarization of html and text using several different algorithms.

A collection of quick-reference sheets for two or three dozen programming languages, from PHP and Python to Standard ML, Erlang, and MATLAB.