For command line apps, the equivalent would probably be statically-compiled binaries you can just drop somewhere in your PATH, e.g. /usr/local/bin/. For programs that are actually built this way (which I would personally call "the correct way") this works great!
If nothing else, consider that the limitations of a statically linked binary match those of a traditional Mac application bundle. While Mac apps are usually dynamically linked, they also include all of their dependencies within the app bundle. I suppose you could argue it's technically possible to open an app bundle and replace one of the dylibs, but this is clearly not an intended use case; if nothing else, you're going to break the code signature.
If the app is not actively maintained, unless trivial, it likely has unpatched vulnerabilities of its own anyway.
And on macOS, if the app is not actively maintained, it usually breaks after a couple major releases regardless of anything else, because Apple doesn't believe in backwards compatibility.