Open Theism is a relatively recent theological movement within Protestantism (the first book to systematically present its beliefs was published in 1994). It seeks to re-define God’s traditional attributes (his omniscience, omnipotence, etc.) in new and decidedly non-traditional ways. Essentially, it’s a radically new philosophical model for understanding God and his relationship to the creation, and is similar in many ways to the Process Theology of Whitehead, Hartshorne, and others.
“…open theists claim that God does not have exhaustive, infallible knowledge of the future, God changes his mind, and God does not exercise providential control over most events. In particular, open theism is troubled by classic Christianity’s commitment to God’s exhaustive knowledge of all future creaturely choices in light of the implications it perceives of this doctrine for human freedom and its own theological and philosophical proposals for dealing with the problem of evil” (God Under Fire, p. 25).
For Catholics, Open Theism’s rejection of the unanimous teaching of the early Church Fathers (from St. Augustine onward), and of the Catholic doctrinal Tradition in general, concerning the nature and attributes of God automatically and unavoidably places it outside the bounds of a genuine (that is, an historically-based) Christian theology. Historically speaking, Open Theism is a speculative and innovative Protestant novelty, which is itself rejected by the vast majority of even Protestant scholarship. It is in no way bound to the historic teachings of the Christian faith, nor does it submit itself to the Church’s 2,000-year-old doctrinal Tradition which has been believed “everywhere, always, and by all.” Open Theism is therefore not a legitimate theological option for Catholics.
I recommend the book quoted above: Douglas Huffman & Eric Johnson, God Under Fire: Modern Scholarship Reinvents God(Zondervan, 2002). Chapter 9 was written by Catholic philosopher Patrick Lee from the Franciscan University of Steubenville.