I have been using the free LibreOffice for a number of years. It can read and write Microsoft Office Word and Excel files and can be set to automatically save in MS Office format. I believe that the only real issue with these files is that Visual Basic macros will not work with LibreOffice.
Also a big fan of Mozilla's Thunderbird email client.
After some 15 to 20 years of using Quicken, I switched to the free
KMyMoney a few months back. While the look is different, the functionality is pretty much the same as Quicken.