A plot generator (sense 1) is found in any set-up which will produce an ongoing series of new cases, issues, etc., as in detective or police serials (incoming criminal cases); medical drama (incoming medical cases); and so on. Even more broadly, "what if" stories can permit writers to introduce any idea they want, as in The Twilight Zone; for obvious reasons, this type of plot generator is found generally in the science fiction and fantasy genres, especially in episodic series which have a villain of the week format.
The idea of plot generators is explored by Nick Lowe in his article The Well Tempered Plot Device Examples he gives include "red kryptonite", which has an unpredictable effect on Superman for 48 hours (conveniently the time period covered by most episodes).
The TARDIS in Doctor Who is the epitome of a plot generator, in that it can take the Doctor anywhere in space and time, where he can encounter anything the writers want him to encounter, from aliens in outer space to famous historical figures.
The Stargate from the movie Stargate, and the television series based on it, Stargate SG-1, is an effective plot generator. By activating and stepping through the gate the characters are taken to any one of a very large unspecified number of alien worlds.
The Holodeck, introduced in the pilot of Star Trek: The Next Generation, could also be viewed as a plot generator, as its open ended nature allowed the show's writers to construct a number of stories later in the series.
Law & Order, and to a lesser extent its spinoffs, has a structure that serves as a plot generator: few episodes are about the characters' interactions with each other; nearly all are about the detectives solving, and the lawyers prosecuting, the mystery at hand.
The television show Sliders featured a device that could send the main characters to any one of infinite alternate dimensions, each episode featured the group appearing in at least one new dimension, which usually had no particular connection to previous episodes.
The Sunnydale Hellmouth in Buffy the Vampire Slayer and the Cardiff spacetime rift in Torchwood act as literal plot generators, explaining the presence of incredibly evil humans, demons, erratic behaviour, magical anomalies etc. or the presence of alien technology, extraterrestrial life, psychic powers and time abnormalities respectively.
The South Park episode Cartoon Wars Part II poked fun at the unusual narrative style of the animated series Family Guy by depicting the source of the show's plot points as a tank of manatees which select "idea balls".
The second type of plot generator is often referred to as a random plot generator, which is represented by a device such as a chart with multiple columns, a book composed of panels that flip independently of one another, or a set of several adjacent reels that spin independently of one another, allowing a writer to randomly select elements of a narrative plot. Such a device can be created for virtually any genre, although it tends to produce formulaic and hackneyed situations.
Plot generators have also been portrayed in fiction, as in Fritz Leiber's The Silver Egghead.
An example from The Official Movie Plot Generator has three vertical boxes. The top specifies a specific type of protagonist, “A trucker who doesn't play by the rules.” The middle box specifies a specific action on the part of the protagonist--”bareknuckle fights for money .” The bottom box specifies a specific type of antagonist, “accompanied by a mischievous orangutan.” By piecing these three elements together, the user obtains the odd sentence, “A trucker who doesn't play by the rules bareknuckle fights for money, accompanied by a mischievous orangutan.” This plot sounds absurd, and it is — but it is also the plot of a movie starring Clint Eastwood — Every Which Way but Loose.
Some random plot generators are designed with particular television series in mind. For example, The Law and Order Random Plot Generator allows its user to select different narrative elements by refreshing the screen. One plot for an episode might read, "A dead infant is discovered in a seedy basement by the perpetrator. Lenny and Curtis initially pin the crime on a local celebrity, but after a visit to the crime lab, they arrest Lenny himself. McCoy and Kincaid prosecute, but McCoy must not push for the death penalty to win. The old DA looks annoyed and says 'A wise person cares not for what he cannot have, but for what he can.' Sting guest stars." By refreshing the screen, the plot reads "A dead taxi driver is discovered in an abandoned van by a police sting. Lenny and Curtis initially pin the crime on a local celebrity, but after Curtis uses an internet chat room, they arrest a co-worker. McCoy and Kincaid prosecute, but McCoy must convict of a lesser crime to win. The old DA looks annoyed and says 'A handful of patience is worth more than a bushel of brains.' Michael Dorn guest stars."
A more current offering for fiction writers is the Plot Generator site, http://www.plot-generator.org.uk, with over 500 million plot variations.