I'm a big fan of LibreOffice for general writing and basic documents are compatible with the more commonly used MS Word. However, advanced features such as 'track changes' and 'styles formats' don't work as well between the different programs.Its fine for starting out, writing drafts, and being sure to always have a word processor on your computer. But, once you get to the point of working with an editor/publisher you will want to invest in the conventionally used commercial program.

LibreOffice 5.0
LibreOffice - The Free Office Suite