The ANSYS 12.0.1 UNIX/Linux Installation Guide no longer makes reference to XFree86, although the ANSYS 11.0 documentation listed the required XFree86 packages, which caused some confusion among users.

Most current Linux distributions use instead of XFree86. Several years ago, XFree86 was the de facto implementation of X11. Because of licensing changes and other issues, two forks of XFree86 occurred, with X.Org Server being one of them.

Now, most distributions use X.Org instead of XFree86. Hence, when installing ANSYS 11.0 or 12.0.1 on more recent Linux distributions, just look for the equivalent X.Org packages instead.