ATI came out with CTM, which was just an assembler. CUDA was released a month or so after that. It was a full C compiler and already had a pretty large set of examples and library functions.

I downloaded CUDA about the day it was released, and used it for real some months later when I bought a 8600 GT GPU.

To call CUDA a response to CTM is too much praise for Nvidia, because it suggests that their response included cobbling a compiler and SDK in just a month. :-)