There's nothing I'm aware of that won't require a CSV export. Even the old AppleWorks/ClarisWorks databases had no good export story besides exporting to a comma separated plaintext ASCII file.
HyperCard might be your best bet. Between the flexibility of its scripting language
HyperTalk (a good primer called the
"HyperTalk Beginner's Guide" shipped with HyperCard 1.2.5, which can be found on
pcamen's site), the
HyperCard Online uploader, and WIP efforts like
MACE to run 68k binaries on modern computers, HyperCard might be the only "database"/RAD development tool with several communities actively devoted to its preservation.
Heading in another direction, if you could find a copy of FileMaker Pro 4.1 for Windows, that should still work with some amount of finagling on Windows 10. The Mac version of FMP4 was the last to run on 68k Macs. I'm not crazy about FileMaker myself, but it ticks the most obvious box of "90s RAD friendly relational database program".
FileMaker has gone in a bit of a subscription-based
RAD in the cloud direction in the many versions since. I don't expect export from modern FileMaker to FMP4 to work well (if at all). They do have
documentation for FMP 4.1 still easily accessible in PDF format, so that's something.
On the other hand, if CSV import and export between two database programs is fine,
Panorama X for Mac OS X is a relational database program from one of the first indie Mac developers that has some great import/export options, tutorials, RAD features, and a subscription model that's intended to be pay for what you use, seems pretty well thought out. Jim Rea, its developer, would probably be interested if you have any ideas for interop with old mac apps. TidBITS gave it
a positive review.
I'm not aware of any other up and coming relational databases. The genre seems to have ossified around the time that $0.99 inventory tracking apps for your phone became a fad.