>>lispm+(OP)
Unfortunately, that one doesn't have 64-bit support (requires a full rewrite to get off of carbon). So no Catalina, but it is very impressive it works on Tiger through Mojave with no hitches! That's 10 versions of the OS.
>>jediea+Sj
Just as an interesting technical note, MacDraw Retro is another one that supports Tiger through Mojave.
And of course, there's a lot of small programs that support the range as well, sometimes just by chance (a Tiger-era program just happens to work), but you're right it's rare for bigger, more-complex stuff.