X11/OpenGL/Redhat

[Peter Bismuti]

I'm a little confused, perhaps someone could get me back on the right track.

Xfree86 has become the standard open source X windowing system that is 
shipped with Linux bundles such as Redhat, but is there a different 
oepn-source implementation from X.org as well?  I got the impression there 
was from a posting I read,  but can't seem to verify whether or not this is 
true.

(aside )  The confusion seems to be that some things that are actually 
defined as protocols (set of rules, API)  but their names are used to refer 
to a specific implementation (i.e. the standard one).  For Linux, is XFree86 
really the only game in town (other than the commercial ones such as XI)? 
Or is there another viable open-source alternative that may contain 
feautures I need and wouldn't take me 3 months to get configured and running 
properly.

Specifically, it seems that currently XFree86 does not support a feature 
that was posted by someone as existing in "X Window System Version 11 
Release 6.8.1".

If not, (if there is something besides XFree86), how simple would it be to 
get it off the ground, configured and running?  (I'm assuming that I could 
kiss Redhat support goodbye, which would be bad, but if necessary...)

The similar confusion exists for OpenGL.  Is Mesa really the only game in 
town for Linux (Redhat Enterprise WS3, again, not counting commercial 
implementations)?  SGI has an open source implementation of OpenGL ported to 
Linux I believe, but is it really practical to choose it over Mesa if 
porting applications to Redhat E3 WS?  Or is Mesa just too integrated with 
Redhat.

In theory XFree86 and Mesa should be decoupled from eachother so each could 
be swapped out with other implementations.  In reality, are they?  Or will 
choosing a different implementaton of each cause me months of headaches?

Perhaps a good commercial version would be worth it as a last reset. 
Specifically, there is functionality in SGIs that is not supported on PC 
hardware and must be emulated in software, such as:

1. dual layers (one layer of pseudo-color or grey scale and another of 
true-color).

2.  12-bit pseudocolor, currently not supported by any PC graphics cards 
that I'm aware of.

Any help would be greatly appreciated.
Thanks in Advance.

Pete