It's our belief that CAL provides an interface to the GPU that is more conducive to GP-GPU programming than OpenGL. It will be tuned more to what AMD/ATI GPUs can offer in terms of computation and functionality.
We are promoting Brook+ as the prefered vehicle for developing your application in. Brook+ is actually derived from (and still feeds back enhancements to) Brook, which is an open-source effort out of Stanford. The nice thing about Brook+ is that not only is it a high-level language, but it tries to abstract away the hardware details so that it is actually possible to retarget to different generations of a GPU and even to different GPUs.
While we are not going to actively spend engineering effort to guarantee compatibility with competitors' products, we are also not actively trying to prevent compatibility. We are, instead, trying to promote a portable high-level programming language which we think is in our customers' best interest.
Michael.
