wf filters its standard input, printing on standard output a list of (frequency, word) pairs, one per line, sorted in order of descending frequency. Words with the same frequency are displayed in alphabetical order.
A word starts with a letter or underscore, and is followed by zero or more letters, underscores, or digits. Letter case is ignored.
This is a handy tool for analyzing writing vocabulary.
Its other purpose is to demonstrate a modest lex(1) program and hashing techniques.