In addition to the examples that Eustace provided, I recently found that AppleWorks v6 that was bundled with many iMacs will also run under OSX. My daughter had immediate need of a computer and no money to buy a new one. I upgraded our unused old iMac 400DV to Panther and added a larger hard drive. As I had no additional licenses for Office and my daughter needed a WP program, I restored AppleWorks from the iMac restore CD to the OS9 partition I made on the new drive.
When I launched AppleWorks, it opened in X, not "Classic." It had a few problems but it basically worked That version was 6.0.4 and the update to v6.2.9 available
here cleared up all the little problems.
Upgrading an office computer to one that ran OSX showed me that any MS Office document created with Office 98 (OS9) would open just fine with Office 2004 (OSX). When you save the document it automatically converts it to the later version unless you tell it not to.
Allan