FreeDWG Viewer - A free program that allows you to view files made with AutoCAD: http://www.infograph.com/products/dwgviewer/

A9CAD - Free software allows you to 2D: http://www.a9tech.com/

DIA - Free, like the famous VISIO, can be used to achieve different types of diagrams: http://hans.breuer.org/dia/default.htm

free2Design - Free software for 2D design that enjoys great appreciation: http://www.free2design.org

GIMP - Free image processing software (free alternative to Photoshop): http://www.gimp.org/

PrimoPDF - Free program for creating PDF documents: http://www.primopdf.com

Inkscape - Free vector graphics software (free alternative to Corel Draw): http://www.inkscape.org/

OpenOffice - Free software compatible with Microsoft Office: http://www.openoffice.org