Freeware (from "free" and "software") is computer software that is available for use at no cost or for an optional fee. Software that is commercial is occasionally referred to as payware.
NB!! Freeware does not necessarily mean open source software. For eg. Sculptris is an example of free software where the source code is not available.
OSS is computer software for which the source code is available. This permits users to use, change, and improve the software, and to redistribute it in modified or unmodified forms. It is very often developed in a public, collaborative manner.
NB!! Open source does not necessarily mean that the software is free.
A free, open-source image editor that provides advanced features close to those of Photoshop.
OpenOffice.org is a free, open-source alternative to commercial office suites. It includes a word processor, spreadsheet, presentations and a database editor. It is compatible with most commercial packages. LibreOffice is a new free, open-source spin off of OpenOffice.
See: http://www.openoffice.org/, http://www.libreoffice.org/
Blender is a free, open source 3D modelling and animation program.