Thus, one can see at a glance how the word behaves in different contexts. Tools differ in the amount of context they can display per word, the size of corpora they can handle, etc.
Some tools provide more sophisticated types of information, e.g. on collocations.
Few provide highly sophisticated means of analysing texts. These run either in a DOS window on a PC or under Unix. Details are forthcoming. Concordancers, KWIC tools, etc.