Upvote:0
You could argue that the New Testament itself is the "other book" in addition to the Old Testament which is based either on the Masoretic text or the Septuagint depending on the tradition.
Upvote:1
For many centuries, The Didache would have qualified. Additionally, today, many denominations use a Prayer Book or a Missal as an aide to the practice of the faith, but as far as doctrine goes, no - it's "The Bible," as defined by the sect.
Upvote:5
It really depends on which branch of Christianity you're asking about.
The Church of Jesus Christ of Latter-Day Saints (Mormons) recognize the Book of Mormon, the Pearl of Great Price, and the Doctrine and Covenants. They also believe in continuing revelation.
Jehovah's Witnesses use the periodic publications of the Watchtower as authoritative.
The Catholic Church recognizes the Deuterocanon as part of the Bible, which most other Christian faiths do not.
The Community of Christ, formerly Reorganized Church of Jesus Christ of Latter-Day Saints, recognizes the Book of Mormon, the Doctrine and Covenants, and the Revised Common Lectionary.
Seventh Day Adventists use the writings of Ellen White.
For a more comprehensive summary, see this article on Wikipedia