Unices is plural of Unix. Some popular Unices include:
  1. FreeBSD
  2. Linux
  3. Solaris
  4. Irix
... but there are many other. One of the main differences windows / Unix is that there is but one source of windoze, but many Unices.

Linguistic note: People who spell UNIX in all caps don't often use the term Unices, but people who spell Unix like Unix often do.