Solaris, HP-UX, AIX, and FreeBSD are all Unix systems. With the exception of FreeBSD they are all also UNIX, because other than FreeBSD the other three are commercial Unix OSes that have been certified and therefore hold a license to use the trademarked name UNIX.

Debian GNU/Linux is a Unix-like system because Linux is not Unix, but it is Unix-like and when combined with a GNU userland is POSIX compliant.