Soulver was actually what inspired LastCalc, but I wanted to bring it to the web, and make it programmable.
OpalCalc looks neat, unlike Soulver it supports functions, and I'm sure it has a few features that LastCalc currently lacks.
However LastCalc has a few features that OpalCalc lacks too, such as support for higher-level datastructures like lists and maps, pattern matching (like Haskell), and the ability to pull data from the web to use in calculations.
So I'm not sure that I would describe OpalCalc as "LastCalc on steroids" by any stretch.