Stated by Jesse Morrell on ‎The Open Theist Reformation: Biblical Open Theism Facebook page:

God is omniscient and therefore He knows reality as it is. The knowledge of God must perfectly correspond to the nature of reality or else He is not omniscient. The debate is not whether God knows the future but what is the future that God knows? Are there alternative possibilities or only certainties? If the future has alternative possibilities, God must know that there are alternative possibilities or events that may or may not occur, otherwise He is not omniscient because He does not know reality as it is.

So omniscience, properly understood, is consistent with free will. God being omniscience knows that we have a free will, He knows that we may or may not do certain things, etc. He does not foreknow all future events as absolute certainties because they are not all absolute certainties. God knows possibilities as possibilities and certainties as certainties.