Taken from the Pine FAQ at http://www.washington.edu/pine/faq/whatis.html -- "Pine's message composition editor is also available as a separate stand-alone program, called PICO. PICO is a very simple and easy-to-use text editor offering paragraph justification, cut/paste, and a spelling checker."
Pico is generally used by those who are new to UNIX, but many experienced users compose email with it as well.
The GNU project has a clone of Pico called Nano. Nano was developed because Pico's license is not considered to be a free software license.