Pure text documents I end up using on client missions:
map.org : Mind map of the project made using org-mode.
journal.md : A day-by-day timeline of what was done/discovered etc. In markdown.
glossary.md : words as understood on the domain. In markdown
contacts.csv : table of people I interact with for the project.
servers.csv : Servers I interact with
report.md : The conlusion report, incremented daily.