Word Processing

Note-Taking
  Evernote: (Mac, Win)
  Gournal: (Linux)
  Mynotex: (Linux)
  Notelab: (Linux, Mac, Win)
  Tomboy: (Linux)
  TreeLine: Notes/Database (Linux, Win)
  Xournal: PDF Annotator (Linux, Mac, Win)
Office Productivity Suites
  Apache OpenOffice: (Linux, Mac, Win)
  Apache OpenOffice: Portable (Win)
  AbiWord: (Linux, Mac, Win)
  AbiWord: Portable (Win)
  Bean: MSW Clone (Mac)
  Calligra: (Linux, Mac, Win)
  CryptPad: (Linux, Mac, Win)
  Etherpad: (Linux, Mac, Win)
  Joeoffice: (Mac, Linux, Win)
  KOffice Suite (Linux, Mac)
  LibreOffice (Linux, Mac, Win)
  LibreOffice: Portable (Win)
  MSWord : Free (Dos)
  NeoOffice: (Mac)
  OnlyOffice (Linux, Mac, Win)
  Siag Office: (Linux, Mac)
  WordPerfect: (Linux )
PDF
  Combine PDF (Mac)
  doPDF: Create, Convert, doPDF (Win)
  Evince: PDF Viewer (Linux)
  Final Page: Post Production (Linux)
  Formulatepro: PDF Editor (Mac)
  GhostView: PDF View (Linux, Mac, Win)
  Ghostscript: PDF View (Linux, Mac, Win)
  gImageReader: Extract Text from PDF (Linux, Mac)
  GSView: PDF View (Linux, Mac, Win)
  ICEpdf: Java PDF (Linux, Mac, Win)
  Jarnal: Notetaker, PDF Annotator (Linux, Mac, Win)
  MacGSView: View (Linux, Mac, Win)
  Master PDF Editor (Linux, Mac, Win)

PDF (continued)
  Okular: Viewer (Linux)
  Pandoc: Converter (Linux, Mac, Win)
  PDF Arranger (Linux)
  PDF Readers & Creators (Linux, Mac, Win)
  PDFedit (Linux)
  PDF Editing Tools (Linux, Mac, Win)
  PDF Extension (Linux, Mac, Win)
  PDF Mix Tool (Linux)
  PDFRead (Linux, Mac, Win)
  PDFsam: Split & Merge (Linux, Win)
  PDF software (Linux, Mac, Win)
  PDFTK:  Build, Join, Split, Rotate (Linux, Mac, Win)
  PDF-Xchange Viewer (Win)
  PoDoFo: Libraries (Linux, Mac, Win)
  QPDF: Transformations (Linux, Mac, Win)
  Sun PDF Import (Linux, Mac, Win)
  SWFTools: Text Tools (Linux, Win)
  Win2PDF: Creator (Win)
  Xpdf: Reader (Linux, Win)
Text Editors
  Antiword: Reader (Linux, Mac, Win)
  Atom: Hackable editor (Linux, Mac, Win)
  Celtx: Screenwriting (Linux, Mac, Win)
  BBedit (see TextWrangler): Mac
  Docutils: Text Processing (Linux)
  Dokuwiki: Wiki (Linux)
  Emacs & Aqua: (Linux, Mac, Win)
  Encryptpad: Secure Text (Linux, Mac, Win)
  Etherpad: Web Editor (Linux, Mac, Win)
  eany: Editor (Linux, Win)
  GEdit: Editor (Linux)
  Glipper: Clipboard (Linux)
  Gmate: Editor (Linux)
  Gtkedit: (Linux)
  Hexeditor: Linux, Mac, Win) 
  JEdit: Editor (Linux, Mac, Win)
  Joe's: Editor (Linux)  
  Kate: Editor (Linux)
  Leaf: Editor (Linux)

Text Editors (Continued)
  Leafpad: Editor (Linux)
  Medit: Editor (Linux, Win)
  Music: Notation (Linux, Mac, Win) 
  Nano: Editor (Linux)
  Nedit: Editor (Linux)
  Notepad2:Text Editor (Win)
  Notepad Plus: Editor (Win)
  NoteTab: HML Editor (Win)
  PyRoom: Editor (Mac, Win)
  SciTE: Editor (Linux, Win)
  reStructuredtext: Markup Syntax (Linux)
  Scribes: Gnome Editor (Linux)
  Sed: Streams Editor (Linux)
  Tea-Editor: (Linux, Win)
  Ted: Editor (Linux)
  Text Editors: Various (Linux, Mac, Win)
  Textroom: Editor (Linux, Mac, Win)
  TextWrangler: (Mac)
  Tiddlywiki: Web Notebook (Linux, Mac, Win)
  TinyMCE: Editor (Linux, Mac, Win) 
  Recode: Converter (Linux)
  Vim: Editor (Linux, Mac, Win)
  WordGrinder (Linux, Mac, Win)
  WordPress: Publishing (Linux, Win)
  Writetype: Writing Made Easy (Linux, Win)
  XML: Editor (Linux, Mac, Win)
  XPad: Editor (Mac)
  Zim : Editor (Linux, Win)
Type Setting
  AUCTeX: Typesetting (Linux, Mac, Win)
  Gummi: Typesetting (Linux, Mac, Win)
  Kile: Typesetting (Linux)
  LaTex: Typesetting (Linux, Win)
  Latex2RTF: Translator (Linux, Mac,Win)
  Lyx: Typesetting (Linux, Mac, Win)
  MiKTeX: Type Setting (Win)
  TeX: Typesetting (Linux, Win)
  TexMacs: Typesetting (Linux, Mac, Win)
  Texmaker: Typesetting (Linux, Mac, Win)