Note: this is for further discussion of the answer given here: http://www.libreoffice.org/get-help/frequently-asked-questions/#whyfree
LibreOffice is free and open source software – Free and open-source software - Wikipedia – developed by a worldwide community. You can use, share and modify the software according to the Mozilla Public License 2.0 (Mozilla Public License, version 2.0). LibreOffice is free because the community around it cares about open standards and breaking down digital divides – creating a world where everyone has access to powerful, open source tools.