Here are a few novels based on the Lord of the Rings. I am listing them chronologically.
Bored of the Rings by Henry Beard and Douglas Kenney
This book was published by the Harvard Lampoon in 1969. It is a parody that uses slapstick comedy and several brand names. Much of the humor is quite coarse, but it's fun to read.
The Iron Tower by Dennis L. McKiernan
This trilogy was published in 1984 and is a pastiche of Middle-earth. While the trilogy is well written, it is definitely LOTR with the serial numbers filed off. The author wrote subsequent novels set in this world.
The Last Ringbearer by Kirill Eskov
This Russian novel published in 1999 puts a different spin on the War of the Ring. Gandalf and the Elves are the villains in this novel. However, as the premise for this novel is that "history is written by the victors," they portray their version (the published LOTR) as the true account of events. I never finished this novel, but it's on my to-do list.