Mathcad 11 was originally designated Mathcad 2003 in the beta1 release. Somehow, in the span of about two months, the beta2 release came out labelled Mathcad 11.
Mathcad 11 adds more functionality in ODE solving and adds some capability in PDE solving.
If you look at the version comparison from Mathsoft, you'll see that 2001i is quite close to 11, but there are some differences:
