We already have lists of general-reference resources, one on meta and a larger one on main. For the most part, these are things like dictionaries and thesauri, not actual tools related to natural language processing (NLP) or computational linguistics (CL). I would like to assemble a list of the most useful tools that come in handy for ELU.
These range from simple two-edged swords like Google Ngrams and the fancier corpus-analytic tools like the BNC or COCA (both of which require some sophistication to use), all the way up to tools for doing part-of-speech (POS) assignments, as well as stemmers, lemmatizers, chunkers, and syntactic analysers (‘parsers’). There are a lot of other interesting ELU-related things it would be nice to know where to find the tools for, too.
For example, given this sentence:
Yes of course the car whose headlights were off was running is right.
One can use the CMU Link Grammar Parser via the CGI form here to generate this parse:
(S Yes (S (PP of course) (S (NP (NP the car) (SBAR (WHNP whose headlights) (S (VP were (PRT off))))) (VP was (VP running is (ADVP right))))) .)
However, another approach is to use the DependenSee visualization tool to generate a PNG of the dependency graph of a given sentence using the Stanford Parser, which looks like this for that same sentence:
Please add a separate answer for each tool, and include both the link and a small demo of what that tool is good for. I find the graphical tools especially useful, and I think a lot of other people do, too: witness the fascination with Google N-grams.
We can use the voting system as a way of showing which tools we think are most or least useful.