The first thing you have to take into account is that people write for many reasons and in many formats. The following short list of possibilities:
love letters, family letters, farewell letters, (there are more than 500 types of letters)
personal diary
family will
informal notes
forms
birthday cards
gift cards
resume
COLLEGE WRITING
essays, informal essays, prose, short story, dialogue, summary, poem
research report
presentation
article for publication in a journal
NEWSPAPER WRITING
editorial
international page article
sports article
wanted ad
obituary, etc.
ELECTRONIC
web page
chat
LEGAL WRITING
birthcertificates
diplomas
wills
legal case