Roger Olson has addressed an interesting question: are open theism and Molinism forms of Arminianism or not? He thinks that open theism is but Molinism is not.
I agree with Roger Olson that open theism is a sub-category of Arminian theology but I disagree with his assessment that Molinism does not belong there. Here is the slightly edited comment I wrote on his blog post (though it has not yet been approved there).
I speak as a Calvinist, but I think you are right to identify open theism as a form of Arminianism. I also think that the more traditional Arminians who want to exclude open theism (deeming it something drastically different because of the denial that God foreknows libertarianly free creaturely choices) are wrong. Their error derives, I think, from overstating the practical difference between open theism and classical Arminianism. I say this because I agree with William Hasker that simple foreknowledge is useless to God because it allows him no opportunity to do anything about what he foreknows. By the time God knows what a creature will do in the future, he also knows what he will do, so there is no room for him to decide how to respond. (This is true even if God is absolutely timeless, so that one is speaking logically rather than chronologically about the order of God’s decrees.) So open theism actually gives God more room for genuine responsive action than simple foreknowledge Arminianism does. God’s activity in the world is thus enhanced, rather than diminished, by open theism.
On the other hand, I disagree with your assessment of the proper location of Moliniasm. It is a type of synergism. As a position that considers freedom to be libertarian, so that the situation in this actual world is indeterministic/incompatibilistic rather than deterministic/ compatibilistic, Molinism (and midddle knowledge) is a live option for Arminians, but not for Calvinists. The usefulness of Molinism within an Arminian framework is even being acknowledged by an open theist such as Greg Boyd, when he speaks of the usefulness of God’s knowledge of “might” counterfactuals, even though he denies that God can know “would” counterfactuals. Incidentally, I agree with him in regard to the grounding objection to Molinism (it is impossible to foreknow what a libertarianly free creature would do unless the creature makes a decision), but I disagree with his critique (and that of many Calvinists) about the possibility of simple foreknowledge of libertarianly free acts. (William Lane Craig, a Molinist, is right to propose that we think of divine foreknowledge propositionally rather than according to the metaphor of sight.)
On the other hand, I doubt that an open theist affirmation of God’s knowledge of might counterfactuals gives God a significant advantage providentially. Even if God could predict with 99% accuracy how libertarianly free creatures would act in every possible situation, the combination of the immense number of decisions that make up human history would not enable God to plan ahead very much. Nonetheless, if I reverted to synergism tomorrow, I would more likely become an open theist than a classic Arminian.