Laxmi Bachanalaya
Legally available public-domain books and openly licensed reading materials.
James McAndrew
Edward J. Ruppelt
Donald H. Menzel and Lyle Gifford Boyd
Donald E. Keyhoe
United States. Federal Bureau of Investigation
Charles Fort
United States. Air Force
William Sambrot
Jr. Sam Merwin
These books are free to read. Each is in the public domain in the United States; check your own country's rules before you copy or share one.