I've never heard of nsjail, so I wouldn't know. But there's also bubblewrap which is used by Flatpak for sandboxing. It's very small, although a bit annoying to use.
Bubblewrap seemed much less user friendly than nsjail, I assume because it is intended to be a lower level application used by libraries like flatpak. It is also more tailored to desktop applications and GUIs, whereas nsjail is focused on server apps (though I did see the author mentioning adding better support for GUIs years ago, but I did not check if that happened).