The short answer is yes. There were others. The longer answer is that the Book of Mormon was actually pretty unique not just in its length, but also in its broad vision, depth/coherence, and impact in forming a community.

To start, I have to say a little bit about the Second Great Awakening. It started around 1800 and lasted until the 1840s. This was a really important time of increased religious fervor in American culture that gave rise to lots of Protestant denominations in America. Mormons, Adventists, Baptists, Methodists, Presbyterians, Shakers, and many other denominations were either established during this time or saw their numbers skyrocket. The classic book on the Second Great Awakening that's still regarded highly in the field is Nathan Hatch's book The Democratization of American Christianity (Yale: 1991).

The Second Great Awakening put a big emphasis on individual interpretations of the Bible, emotional religion, and the ordinary person's ability to discern religious truth. They strongly emphasized the importance of conversion. In that context, there were all kinds of prophets, visionaries, and leaders claiming to have received religious revelations of some kind or another. These leaders often came from "nontraditional" or "non-elite" backgrounds, just like Joseph Smith. Their religious authority came from their personal charisma, the emotional power of their message, and their ability to build a community around them. And, very often, they claimed their religious authority came from personal, direct encounters with God. Sometimes, they wrote scriptures. But it wasn't very common. Some other examples of these kinds of self-appointed, visionary leaders include: i) Mother Ann Lee, the founder of the Shakers, a widow who claimed to be the female incarnation of Jesus and said Christians should be celibate; ii) Richard Allen, the founder of the African Methodist Episcopal Church, a former slave who started a powerful Black institution that is still very influential today; and iii) Lorenzo Dow, a long-haired Methodist preacher on the frontiers who often shouted and jumped around to sway the emotions of congregations. There are lots of other examples of similar leaders from this period.

Joseph Smith falls into a similar category of "outsider" leaders whose religious authority did not derive from formal credentials or pedigree. He was a visionary and prophet whose authority was said to come from his direct encounters with God, Jesus, and angels. He used his personal charisma and emotional preaching to convince others his message was genuine.

Smith was the son of a repeatedly failed farmer. He had almost no formal education and absolutely no traditional credentials. He said that while he was still a teenager, he had a vision of God and Jesus. According to Smith, they told him he would become the prophet of a new church that would correct all the errors in other kinds of Christianity. Later, he said he had other visions--this time of an angel named Moroni, the son of a prophet named Mormon. According to the LDS tradition, the angel Moroni led him to a place in the woods near his home where he found Golden Plates buried in a hill. These plates were said to contain a lost scripture, written in a mysterious language Smith identified as "Reformed Egyptian." According to the tradition, Smith was provided with the miraculous means to translate these Golden Plates. The result was the Book of Mormon, first published in 1830. It told a grand, sweeping tale about two lost tribes of Israel that made their way to the United States.

It reads very much like books of Kings and Chronicles in the Old Testament. In the Book of Mormon, these two powerful tribes fight wars against each other. One group becomes evil, the other good. Eventually, all the evil ones kill all the good ones. The last survivors of the good tribe are the prophet Mormon and his son, Moroni. In the Book of Mormon, they bury the Golden Plates in the hopes that a prophet will arise in the "latter days" who will restore true Christianity.

So, in short, the Book of Mormon developed a highly elaborate theology and told lots of stories that appealed to 19th-century Americans. Regardless of its religious impact, it was a major literary accomplishment. Among many other things, people of the time loved that it explained the origins of Native Americans as one of the Lost Tribes. It set the grand story of salvation firmly in the American context. It even said that Jesus preached in America after his resurrection. The Book of Mormon formed the bedrock of the church Smith established, the Church of Jesus Christ of Latter-day Saints (Mormons).

Whatever you think of Mormonism, it's a pretty incredible story. Either Joseph Smith miraculously translated a lost scripture (the LDS interpretation), or an uneducated farmer's son wrote one of the most influential works of American literature ever written (a more skeptical interpretation). In that sense, the Book of Mormon is basically unique. There really aren't a lot of similar religious works of the 19th century that can claim to have its scope, breadth, depth, and coherent literary vision--all from the pen of a guy who was basically an uneducated country bumpkin. For more info on the (very interesting) life of Joseph Smith, see: Richard Bushman, Joseph Smith: Rough Stone Rolling (2007).

Now that we have a little bit of context in place, we can talk about some comparable works. Again, I do think the Book of Mormon is a bit of an outlier, just because it's so grand and complex of a literary achievement. Plus, it's still important today and regarded as scripture by the LDS church. But there were other similar works created in the 19th century by unlikely visionaries, prophets, and "outsider" religious leaders. One that immediately comes to mind are the writings of Ellen G. White, the founder of the Seventh-day Adventist church. She wrote prolifically throughout her lifetime about her visions of God and her interpretations of Christian doctrine (such as the idea that Christians should be vegetarians). Some titles by her include, Steps to Christ and The Desire of Ages. Today, these are still read alongside the Bible by Seventh-day Adventists as important religious texts. Another 19th century book that holds a similar status as scripture for a specific community is Mary Baker Eddy's Science and Health with Key to the Scriptures (1875). I don't know the exact number of words, but that thing is really, really, ridiculously long (a modern edition runs 700+ pages). Mary Baker Eddy founded the Christian Science movement. It's often confused with Scientology, but is something different. If you've ever been to a big city in the northern US, you'll usually find a Christian science "reading room" or a big fancy church called "Church of Christ, Scientist." This post is getting too long to explain her religious ideas fully, but basically Eddy taught a type of "mind cure" (that the mind/faith can cure all disease). Her writings in Science and Health are still highly regarded by Christian Scientists today. But in contrast to Mormonism, the Christian Science church has always been very small (never more than a few dozen thousand members). The Mormons have grown pretty consistently since the church was founded by Joseph Smith in 1830. Today, there are over 16 million Mormons.

Tl;dr - Book of Mormon is pretty unique, but not completely unique.

Hope that helps.

Edited for grammar and to remove some grumpy nonsense.