What is the best replacement for AppleWorks?

No, they aren't actually built-in, but you can download Pages, Numbers and Keynote from the App Store if you have a compatible Mac with a supported macOS version.

Pages

https://apps.apple.com/us/app/pages/id409201541?mt=12

Numbers

https://apps.apple.com/us/app/numbers/id409203825?mt=12

Keynote

https://apps.apple.com/us/app/keynote/id409183694?mt=12

If you have an older Mac and need an office suite, LibreOffice is free and pretty powerful and works on macOS versions as old as 10.15 Catalina.

https://www.libreoffice.org/

Pages, numbers, keynote are all built-in to Macs.

There is no replacement owing to the proprietary tool integration in AppleWorks. And, the more tools one used, the lower the chance of converting the document to something else.

The Pages, Numbers, and Keynote '09 applications could open AppleWorks 6 documents when those documents only used the word processor, spreadsheet, or presentation tools respectively. Versions of these Apple applications released after Oct 2013 cannot open any AppleWorks documents. Current versions of these applications do not handle the old PICT images either.

The free LibreOffice Suite (not OpenOffice) can open (read-only) both Mac and Windows-sourced ClarisWorks 5/AppleWorks 6 documents. The ability to achieve this goes back to the first paragraph and dwindles by the number of tools one used in the source documents. AppleWorks database content will be written into LibreOffice Calc as spreadsheet data without formulas. PICT images are not handled and will result in a white box.