I put Kalecki in the "simultaneous discovery" category rather than the predecessor category, but he needs to be noted in light of the last post. Kalecki is right there with Hicks as a guy that could have been Keynes if there was no Keynes.
Kaleckian models are also a good illustration of my point in the last post about the difference between a theory and a model. If you figure that many models can operationalize Keynes's theory, Kaleckian models are also good competitors with Hicksian (and for that matter New Keynesian models) as an operationalization of the foundational Keynesian theory.
Kaleckian models are very good for thinking about the macroeconomics of income distribution. They're also good at operationalizing Keynes's idea that wage cuts are not always the answer, because these models allow for what is called "wage led" and "profit led" growth.