Because Christianity is so intertwined with Western culture, some New Religious Movements may borrow aspects of Christianity or may be derived from Christian denominations.
The Unitarian Universalist Association of Churches (Is a Christian in this organization Christian or Unitarian Universalist? Would all members count or just the self-identifying "Christian" members?)
Religious Science (This religious organization uses the Bible as a holy text and has a statement of faith that appears to be very similar to Christianity. Do these people call themselves Christian or just vaguely spiritual? Wikipedia reports that the group uses The Science of Mind and the Bible, presumably including the New Testament, as part of the scriptures, in much the same way as Christian Science and Mormonism; however, the latter two organizations actually call themselves "Christian".)
Messianic Judaism (Is this thing Jewish or Christian? Although mainstream Jews will certainly reject them and mainstream Christians may view them as Christians, the line is really blurred when you consider that some adherents are actually Jewish and adhere to Jewish Law. Now what?)
Church of Scientology (Is this a church or not? Are Scientologists even Christian? Why does the Scientologist cross resemble the Christian Latin cross?)
People's Temple (Although this is indeed a Christian church, I don't think you would find adherents today. If there are SE questions pertaining to this organization, then they must be done exclusively by outsiders, unless there happens to be a survivor.)
Alcoholics Anonymous (This is definitely not a church. But it has these spiritual things that resemble a church, and many meetings take place in churches. They even have this Serenity Prayer. Although this self-help group means well, some people may feel uncomfortable with its overt spiritual tendencies. Plus, the beliefs of this "Higher Power" seem to coincide with Christianity's God.)