BSD

Linux

Minix

GNU/Hurd

Plan 9

Solaris

OpenVMS

OS X

AIX

HP-UX

Windows

HP-UX 11i

HP-UX is a proprietary UNIX operating system developed and sold by Hewlet Packard.
Like AIX, HP sells hardware resources that can be activated on demand.
You buy a machine that has some of it's hardware locked down by HP, if you want to activate it you pay them.
You can also have them charge you based on how much system resources you use.