The Millenium Group has an ongoing rivalry with the Toastbusters. The Toastbusters were founded partly in response to the feud between the Wieners and Anti-Wieners, to keep both from getting completely out of hand. However, the Toastbusters are completely unsubtle -- they have a tendency to go in guns blazing, and don't understand the notion of keeping things under wraps. The Group regards the Busters as naive fools; the Busters think of the Group as kind of creepy, and probably pretty suspicious themselves. They are each others' principal rivals, although both have lots of other targets.
The Toastbusters have been investigating both the Wieners and Anti-Wieners, on the theory that both have been contaminated by out-of-control, rabid yeast products. The propensity for both to be eaten on "rolls" concerns the Busters greatly; they have a unit trying to divine the true, sinister purpose of "rolls". They suspect alien influence on Earth's wheat crop over recent decades. They have begun to suspect that the Church of Elvis is behind this, but recent rumors about Space Pirates attacking the Earth have led them down new paths. They suspect close relations between the two groups, and think that the Church is simply a front for the Pirates, who are trying to take over the Earth.
The Church and the Pirates are, in fact, long-time arch-rivals. Elvis was recruited by the alien Space Brigade decades ago, to lead the fight against the Bad Guys. The last time the Pirates visited Earth on a raiding trip, they accidentally killed the Lenape Indians of the mid-Atlantic, swamping their rafts. The Brigade was investigating, and Elvis -- who was looking for a good cause to get him out of Las Vegas -- happened to get involved. Through his quick thinking and great tunes, he quickly rose to the field leader of the Brigade. The Pirates were, in fact, being chased by his flagship when they were spun out of control by the Chaos Vortices. The two groups don't know each other directly, but know enough to harbor deep animosity.
The Church was created by those who saw Elvis during one of his fairly frequent trips. (Specifically, it was created after the end of Where There's a Will.) As Elvis has been sighted more and more over the decades, more people have been touched by him, and drawn to the Church, until it has become a thriving sect. The Church is quite aboveground, led by ???, a charismatic preacher who has been recruiting steadily. Not everyone believes that he is a true believer, however -- some within the Church suspect that he is actually a False Singer, distracting from the true, tender lessons of The King. The Church has heard a bit about the Space Pirates over the years -- they don't know many details, but they do know that Elvis has been chasing them because they are evil, nasty, and detest rock and roll.
The Pirate do, in fact, detest rock and roll as it was taught by Elvis -- they prefer (metal? alternative? Something moderately different from traditional rock.) A constant point of contention has been Elvis' strategy of blasting his songs over all subspace frequencies to distract and annoy the Pirates, and shoot them down. They really aren't such bad folks; they are classic freebooters, who don't like the degree to which the galaxy has become civilized. They regard it as their mission to keep things more interesting and entertaining, and think that a few people getting a little hurt is simply the way of life. They don't usually deliberately kill, though; it's sometimes the way things work out, but in general they prefer only to kill in honorable ways, like duels. They know about the Church through the most obvious ways: you can't easily miss them. The Pirates are appalled that this planet has so quickly come to worship their worst enemy, the anti-(musician), and regard it as their sacred mission to do something about it (all in the spirit of fun, of course).
(Alternative: the Pirates are essentially out of Penzance, and have a tendency to break into light operatic song at the drop of a hat.)
The Luddites are opposed to all this hyper-science stuff that has been springing up in recent years. They don't regard aliens as evil because they're aliens -- they're evil because they use super-science. Science corrupts the world in a wide variety of ways. People come to worship it at the cost of Real Values like hard work. If beating eggs was good enough for their grandmothers, then it's clear that electric mixers are works of the Devil. They are also pretty public, and tend to lecture on every soapbox they can find. (They don't proselytize over the Net, of course -- soapboxes are the way God meant for Truth to be spread.) They are particular opponents of the Church of Elvis, but they also detest the Toastbusters, whose aims may sometimes be laudable, but whose means are terrible. There is a strong crossover between them and the Millenium Group, who share some similarly extreme views.
Those in Black were originally the High Priests of Lemuria, who were allied with those of Atlantis when both were sunk by the Followers of Set. Their great powers came from super-science; they were originally half-breeds with aliens, four thousand years ago. They brought the beginnings of civilization and science to humankind then, combatting the evil forces of superstition and "magic". Magic is actually extradimensional forces, brought through to this dimension through arcane rituals. It tends to weaken spacetime, and harm scientific causality; it is harmful even in small doses, and can be devastating in larger ones. The Lemurians (the name of the original planet that the Priests came from thousands of years ago) have seen innumerable worlds destroyed by the use of magic, including their own, devastated through the experiments of Set, a magician from ages agone. They know that the Followers of Set are a church founded on sand, but the Followers have no desire to listen to reason.
The Followers, of course, have a completely different view of history. They have heard the lies of Those in Black, of course, but know that Set was actually a god, who taught his chosen people the ways of power. Those in Black are demons (why else do they dress in black?), who seek to destroy the magic, and overrun the world with their evil Science. The Followers have had a few tactical alliances with the Luddites, with whom they share an opposition to Science. Of course, the Luddites would be appalled if they knew the full truth about the Followers, who are pretty ungodly themselves. The Followers have been occasionally masquerading as Luddites, and a few have adopted most of the Luddite credo, but in general they think of themselves as using the Luddites.
The Interactive Literature Foundation are, essentially, the Timelords.
They are the ones charged with keeping the fabric of spacetime intact and
stable, and preventing an excessive number of cross-dimensional incursions.
They are allied with the other forces of order, particularly the Millenium
Group. Essentially, the Group works on dealing with a number of the
symptoms of dimensional Vortices, while the ILF deals with the root causes.
The Foundation is somewhat opposed to (or, at least, monitors) all of the
strange groups, constantly evaluating their effects upon the continuum.
Their only deep enemies are the Followers, whose magic tends to be highly
destabilizing to the proper functioning of spacetime. They have an
ancient rivalry with Those in Black, despite being fairly natural allies.
There was an incident some years ago, where the two groups conflicted in
their styles, and which led to discomfort between them. (Broadly
speaking, Those in Black are opposed to all forms of Magic -- that is,
cross-dimensional force transport -- whereas the Foundation regards limited
crossover as necessary, but in a controlled way.)