Charter ITC / Bitstream ?

I was looking for the Charter font from Matthew Carter and discovered that there are multiple versions.
I wonder if someone can tell me what are the differences between the 3 listed here (in terms of design, not concerning the rights to sell) :

ITC Charter (Linotype) (ITC Charter Regular - $35)
ITC Charter (ITC) (Charter Regular - $29)
Charter BT (Bitstream) (Charter Regular - $24.75)

Thanks for your help

Charis adjustments - willing to share?


Preamble: Charis is a free font from SIL and legally based on Charter. More info:

I've been using Charis for some time now and every once a while I adjust it some more to my liking. I know that some you did your own modifications (e.g. Charles Ellertson, Richard Fink), are you willing to share your version of the font?

To set a good example, here is my version – unoriginally renamed to “Charta” (German for “charter”) since modified versions must be renamed according to the SIL license.

What I changed (as far as I remember):
- Added kerning
- Respaced the italics (Charis' italics are too tight, in my opinion)
- Slightly emboldened the superscript numbers