The document lists over 80 functions available in the REXX programming language, including functions to manipulate strings, numbers, dates, storage, and streams. Some key functions are ABS to return the absolute value of a number, DATE to return the current date, LENGTH to return the length of a string, SUBSTR to extract a substring, and VALUE to query or change the value of a variable. The functions provide capabilities for text manipulation, mathematical operations, programming logic, and interacting with the operating environment.