byobu has a Homebrew package, but sadly, there’s no MacPorts port. Luckily, byobu is Mac friendly, and only requires a few dependencies (gleaned from an old portfile and crosschecked w/ the homebrew formula):
port install python27 gettext libnewt coreutils gsed
Then it’s just a matter of grabbing the latest tarball, and running a
configure && make && make install.