LibreOffice is a free and open source office suite developed by The Document Foundation. It was forked from OpenOffice.org in 2010, which was an open-sourced version of the earlier StarOffice. I have been using this program now for a couple of years and so far don't have a single complaint.
LibreOffice takes the place of Microsoft Office which will set you back well over $100. The LibreOffice suite comprises programs for word processing, spreadsheets, slideshows, drawings, databases, and composing mathematical formula. It is available in 110 languages. AND...it's compatible with any document created in Office. For example, you can save and/or load in any of the following word documents in these formats: .odt, .ott, .fodt, .uot, .docx, .xml, .doc, .dot, .xml, .html, .rtf, .txt, .docx. If you need help it is very well documented.
LibreOffice uses the international ISO/IEC standard OpenDocument file format as its native format to save documents for all of its applications, but perhaps more importantly, it supports all major competing office suite applications (proprietary and open source). LibreOffice is also compatible with other major office suites, including Microsoft Office.
LibreOffice is available for a variety of computing platforms including Microsoft Windows, OS X (10.8 or newer), and Linux (including a LibreOffice Viewer for Android.
If you're a math person, it has an application designed for creating and editing mathematical formulas. These formulas can be incorporated into other documents in the LibreOffice suite, such as those created by Writer or Calc, by embedding the formulas into the document.
The database program is similar to Microsoft Access.
A wide assortment of templates are available for download, too. Take a look at the list of what's available: Accounting, Agenda, Arts,Book, Brochure/Pamphlet, Budget, Business, Calendar, Card, Resume, CD/DVD, Certificate, Checkbook, Christmas, Computer, Conferences, E-book, Education, Academia, Elementary/Secondary School, Envelope, Fax, Genealogy, Grocery, Invoice, Labels, Letter, Magazine, Media, Medical, Memo, Music, Newsletter, Notes, Paper, Presentation, Recipe, Science, Sports, Timeline, Timesheet, Trades, To Do List and Writer.