LibreOffice
LibreOffice from the Document Foundation is a free office suite that is a suitable replacement for Microsoft Office. The software is free, and works on all platforms.
LibreOffice is able to read and write documents in Microsoft Office formats; enabling you to share your work with people using Microsoft Office. There isn't 100% "round-trip" compatibility between LibreOffice and Microsoft Office. LO has features that MO isn't capable of, and vice versa[1]. So, in some settings you may be forced to purchase Microsoft Office. Beware that Microsoft Office isn't even compatible with itself if you compare the Windows version to the Mac version to the "rental" Office365 version.
LibreOffice also exports PDF documents with a single click; so if you simply want to publish a finished product, you can easily share a pdf file with others.
It is also based on a completely open file format so that your documents will never become hostage to the vendor. LibreOffice is a next generation version of OpenOffice which was taken over by Oracle Corporation when they bought out Sun Microsystems (the primary developer of OpenOffice at the time).
Working with remote Data Sources, you can pair the desktop convenience of Calc spreadsheets or Writer form letters with important data that resides in other applications.
