There are a bunch of GNOME/Gtk applications that are useful in an office enviroment.
Standard Office Applications
AbiWord - Word processor (supports also OpenDocument Format).
Evince - Document viewer (official part of GNOME).
Evolution - Groupware and Email application (official part of GNOME).
Gnumeric - Spreadsheet application.
Inkscape - Vector Graphics and Presentation Creations
Ease - Presentations (using Clutter, in development)
Other GNOME/Gtk Office Applications
GnuCash - financial application
gLabels - label designer
Glom - database designer similar to Filemaker
Dia - diagram creation
Related
Tomboy - Note taker
OpenDocument Format (ODF).
Office related Libraries
- libgda
- libgnomedb