If you want to concentrate in the first instance upon writing and organization, not how things will look, nothing beats a (La)TeX system. You use mark-up when writing. Then when you process the source with the TeX system, you get gorgeous output. And you can have considerable control over appearance. Ultimate output can be, in among other forms, PDF.
For scientific writing and publishing, nothing can (La)TeX for typesetting formulas correctly. But the range of document types for which LaTeX produces excellent results is much wider than that, including, e.g., parallel-columns with two languages, including many non-European ones.
You can get such a system for free: see
http://www.tug.org/mactex/2011/.
(Note: the 2012 release is just a few weeks away.)