Open AppleWorks spreadsheets in Mac OS X when Numbers won't work
These files will open just fine in LibreOffice. Mac OS X (tested on OS X 10.11.5) does recognize that each of the files I want to open is an "AppleWorks Document" (as can be seen in the "Kind" column in Finder.app), but it does not know that LibreOffice can open it.

After you've downloaded and installed LibreOffice, there are a few more steps to get them open:


Right click on the AppleWorks document you want to open.
From the contextual menu's "Open With" submenu, select "Other…".


This will open the "Choose Application" window.  In that window:


From the "Enable" pulldown menu, select "All Applications".
If you want LibreOffice to automatically open this document going forward, check "Always Open With".
Select LibreOffice.  You'll get a warning staying that "It's not known if this application can open" the document. Don't worry about that!
Click "Open".


You should now be looking at a well-formatted spreadsheet in LibreOffice. It looks like the original formatting has been maintained; the spreadsheets I opened have colors, italic, bold, etc.

Once you've got it open in LibreOffice, from the "File" menu select "Save As" and you'll have the option to save it in any number of supported formats, such as Excel. Once that's done, your AppleWorks spreadsheet data has been brought into the modern world.

If you always want AppleWorks docs to open with LibreOffice, follow these instructions.