In researching this U&L Q&A titled: permission denied for ptrace under GDB, the question came up, "Is there other software similar to SELinux & AppArmor?".
User @IwillnotexistIdonotexist mentioned 2 that I'd never heard of: Smack & Yama. He found them by searching through the Linux source code. So now we're up to 4.
Are there others?