People here might find interesting that on the Project Gutenberg website of free ebooks (
www.gutenberg.org.) are 2 Tolkien related books, one authored by him.
The book authored by him is his
A Middle English Vocabulary, published by Clarendon Press in 1922, and his earliest professional publication.
The second book is
A Spring Harvest, published by Erskine McDonald in 1918. It is a collection of poems by Geoffrey Bache Smith, killed in action in 1916, one of the Tea Club and Barrovian Society, and friend of Tolkien, who edited the book and wrote a prefatory note at the beginning.