Broken terminal - [forkpty: Resource temporarily unavailable][Could not create a new process and open a pseudo-tty.]

I simply restarted my computer to resolve the issue. Hope this helps anyone else in the future.

This explination gives slightly more insight into what id goin on. It seems you have too many processes running on your computer and there are certain limits in place.

http://blog.ghostinthemachines.com/2010/01/19/mac-os-x-fork-resource-temporarily-unavailable/

sudo sysctl kern.tty.ptmx_max=255 (or 511, or whatever) should fix it.

My default (in El Capitan) was 127. (As a tmux user, I need more than that.)

To learn more:

sysctl | grep max
ulimit -a
launchctl limit

cat /private/etc/launchd.conf
cat /private/etc/sysctl.conf

man 8 sysctl