Apache OpenOffice
This open-source Office suite has been around for about 20 years; it comes with a ton of supported languages, your standard Word, Excel, and PowerPoint alternatives, and a bunch of extensions to help you work more efficiently.
The user interface will make anyone familiar with Microsoft Office feel right at home, and OpenOffice is compatible with all common file types. It will run on Windows, Linux, MacOS, and even Sun Solaris.
It's best to view OpenOffice as a community project — anyone can suggest fixes or optimizations, and bugs are dealt with promptly. OpenOffice is, and always will be, completely free.
Mac 10.7 and up
https://sourceforge.net/projects/openofficeorg.mirror/files/4.1.5/binaries/en-US/Apache_OpenOffice_4.1.5_MacOS_x86-64_install_en-US.dmg/download