Ghosts are mentioned in the forum title, so let's get with it here. No, I have never seen one.
"I don't believe in ghosts" is one of those inane statements people make all the time in an effort to seem intellectually superior. Actually, they reveal that they are uninformed dolts. Ghosts are a well-documented phenomenon that cannot be denied. "I don't believe ghosts are evidence of survival after death" would be an intellectually defensible statement, or even "I don't believe ghosts are a supernatural phenomenon."
Ghosts are often confused with apparitions. The classic ghost is a figure (usually human, but sometimes animal) that seems attached to a particular place, unaware of or uninterested in its surroundings, and repetitive in its actions. I have no real idea as to what a ghost is, but it seems to be more a "remnant" or "memory" of what was once a life than a fully-formed spectral representation of a life. My guess would be that this is what most ghosts are - i.e., some sort of electrical remnant or imprint, more like a video than a person.
There are, however, exceptions. Some that more closely fit the profile of ghosts than apparitions DO seem to have some level of awareness and DO interact, albeit in a minimal way, with their surroundings or observers. So there may be some sort of sliding scale of ghostliness.
One popular notion is that ghosts are "trapped" by past deeds or experiences and can be "freed" or "released" by psychic intervention. I doubt it, but maybe. (Ghost Hunter-type TV programs are ridiculous from top to bottom and not to be taken seriously. Dr. Payette has been a member of both the (British) Society for Psychical Research and the American Society for Psychical Research, so you can pretty much take what he says as Ghost Gospel.

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Apparitions are a different story. They do not appear repetitively. They may be fully formed, indistinguishable from living persons. They may be observed by multiple persons, and their reflections may be seen in mirrors. Sometimes they deliver very meaningful messages and information. They are something entirely different, and the 100 or 1000 best cases (out of millions) would constitute compelling
prima facie evidence of survival after death.
It is suspected that, real as apparitions may seem, they may involve some sort of telepathic link between the observer and the apparition. In some cases, the apparition is seen by one or more observers and not by others.
I've never seen an apparition either, unless you count my dog Dusty as described above. However, I did experience a couple of pretty convincing ADCs from my wife's relatives. "Why would they communicate with YOU and not with ME?" she pouted, since I wasn't particularly close to them. My best guess at an explanation was that some people are, for whatever reason, simply better "receivers" and the deceased make use of whomever they can reach.
One of the stories I heard personally was from Michelle, a longtime Mormon secretary in my office. She was upstairs in the middle of the afternoon, sitting on the bed, fully lucid and worrying about the baby she was carrying. Her late father-in-law, whom she had never met and knew only from photos, materialized at the foot of the bed, big as life, simply smiled and said "It'll be OK," and dematerialized in front of her eyes. Astonishing as this may sound, it wouldn't even make the cut of the 10,000 most impressive and well-documented cases.