J.R.R. Tolkien's Riders of Rohan is an abandoned DOS fantasy strategy game set in the The Lord of the Rings universe, developed by Papyrus Design Group, designed by Hank Howie, Adam Levesque, Phil Redmond and published by Mirrorsoft in 1997.
J.R.R. Tolkien's Riders of Rohan was based on a novel. It's available for download.