It should be very possible to build something that runs on any version of OS X/macOS, so about 20 years.

I hadn't quite put together how much desktop computing changed between 1994 (DOS, Windows 3.1, System 7) and 2001 (OS X, Windows XP), and how relatively little it's changed since then.

As someone born in 2001… yeah. Wow.

I don't think the PPC emulator ships with osx anymore.

Did the initial versions of osx recognize fat binaries or was that explicitly introduced later?

XNU has had support for fat binaries since NeXTSTEP.

I think fat/universal binary trickery might be able to do it?

"Universal" Mach-O binaries are specific to the Mach-O binary format, which wasn't supported on classic Mac OS. (I'm not even sure that multiplatform executables were even supported by Mac OS X before 10.4 or so, when they started using them for Intel cross-compatibitility.)

"Fat" CFM/PEF binaries existed on classic Mac OS, but used a completely different mechanism that only supported 68k and PowerPC code. And if you wanted to support a Classic II, that rules out a Carbon application bundle too.

About the widest range I can imagine for a single executable is a hybrid CFM/PEF/Carbon executable, which might be able to run on anything from a classic 68k mac up to Mac OS 10.6 (through Rosetta).

For the specific request here (Classic II and current MacBook), you might be able to build an executable with Mach-O data fork and the 68k code in the resource fork. I’m not sure offhand how to make the bundle format work for current macOS, though.

But if you can make that work, you can also add classic PowerPC support, by jumping to it via a 68K CODE stub and perhaps from a separate PEF fragment stored in a section in the Mach-O that would be ignored on current macOS.

I believe multi-platform executables date back to NeXTStep, which supported 68K/x86/Sparc/HPPA binaries.

...Perhaps we’re targeting the wrong product lines. I wonder if you could make a binary that runs across all OS X but also NextStep...

Shameless self-promotion: https://github.com/saagarjha/dummy_thicc. That reminds me that I have left PRs for the NeXTSTEP slices hanging around for quite a while…

Neat. I have a NeXT Station Turbo (68040/33, I think?) and am tempted to try this out.

Oh, this is perfect! Thanks for sharing!

Java?

Macintosh Runtime for Java up to version 1.5.1 requires an ‘030 and System 7.1, so that would be technically possible on a Classic Ⅱ. You would be limited to Java 1.0 API with no JIT, because MRJ 2.0 requires an ‘040 or PPC for that.

<3 that you left the (Motorola) 68k implicit so that those not in the loop will have a hard time figuring out what is actually being discussed

Hard to break old habits :)

I mean, it's doom. You can literally do it in javascript on the browser.

But that's emulated. Emulating a popular video game on a major platform from 1993 isn't all that crazy (not to understate how tricking writing an emulator can be). Having a binary that works on modern hardware and 25+ year old hardware is what's impressive, and it's small enough to fit on a floppy.