GNU Screen is a virtual console multiplexer, and it has long been available on Mac. However, it was developed with login names of 20 characters or less in mind. Nowadays it is possible that login names actually exceed the 20 character limit (for example when using Active Directory), resulting in Screen quiting with the nice error message LoginName too long - sorry and rendering Screen useless on these Macs.
Below are the steps to download, patch and compile screen yourself to allow login names of up to 255 characters.
$ cvs -z3 -d:pserver:anonymous@cvs.savannah.gnu.org:/sources/screen co screen
$ cd screen/src
$ curl "https://raw.github.com/pclouds/pclouds-overlay/master/app-misc/screen/files/4.0.3-extend-d_termname-ng2.patch"|patch
$ for x in Makefile.in config.h.in configure process.c pty.c screen.cc windows.c; do
curl "http://www.opensource.apple.com/source/screen/screen-16/patches/${x}.diff?txt" | patch