"Chaos is the only true answer."
The Xaositects (kay-OH-si-tects), or Chaosmen, are a faction from Planescape. In essence, these barmies believe that there is no meaning to the Multiverse - not that there is no point, like the Bleak Cabal, but rather that things like order, patterns, etc. are all just flukes in an ever-changing and fundamentally unpredictable multiverse. They preach that Chaos is all that there really is - total blind chance, random luck, pure whimsy. Nothing makes any sense because the Multiverse isn't supposed to make any sense. So, people should just accept that, and embrace Chaos as the only universal truth! Do whatever the hell you want; if you feel like doing it, then you should, because there's no reason not to do so.
...If this is ringing alarm bells in your head, then yes: this is basically a philosophy that worships the idea of Chaotic Stupid, and actually considers this the ideal way to behave. Consequently, "I want to play a Xaositect!" is generally met with the same alarm and hostility as the phrase "I want to play a Kender!"
In 2nd edition, belonging to the Xaositects required a Chaotic character alignment, forbade a character from participating in activities that required long-term organization or discipline, made them freakishly adept at knowing instinctively where lost things were, and let them cast Babble (a reversed version of the Wizard spell Tongues) 1/week for basic membership. Those who attained the next rank (Boss) gained Nondection against Divination spells cast by Lawful sources at level 5, and the ability to shoot off a Confusion spell 1/day that hits anyone within 20 feet and lasts for 2D6 rounds; Lawful characters are -2 to their saving throws against this effect. Big Bosses can have all sorts of weird powers, like Wand of Wonder, a permanent Unseen Servant or Alter Self at random.
In 3rd edition, Xaositect was a prestige class issued in Dragon Magazine #287. It required a Chaotic alignment, BAB +4 and +2s in all saves. It has an appropriately random grab-bag assortment of abilities, including protection from divination by Lawful casters, a vocalizing-nixing ability called Babble, dice-rerolling, resistance to Lawful-aligned spells, immunity to Illusion (Pattern) spells, a Confusion aura, a touch attack that compels random actions in victims, a Chaos Hammer spell-like ability, increased difficulty in hitting, and a permanent Protection from Law effect.
In 3.5th Edition, Xaositects got another prestige class from the Planar Handbook, called the Chaotician. Once again requiring a Chaotic alignment, this warrior-based class lets characters infect others with chaotic impulses that made it harder to defend against attacks by the infector, and eventually get a temporary but undispellable miss chance against all non-area-of-effect attacks on the Chaotician by moving very unpredictably. Similar but not identical to the previous versions of this prestige class, Chaoticians get a resistance to Illusion (Pattern) spells (not immunity), a sound-and-speech scrambling ability called Babble that also nullified sonic damage of any kind, and the ability to call upon Chaos to force one reroll a day, either for the Chaotician using the ability or another creature with no saving throw allowed. As an added bonus for players, LOLRANDOM behaviour is no longer encouraged or required for Xaositects in this edition, just an appreciation for (or perhaps even obsession with) the beauty in chaos and a desire to control it.
Xaositects are most known for (aside being a pain in the ass) their use of Scramblespeak, a bizarre verbal cipher in which random words are jumbled out of order in various sentences at random, which is likely decipherable only to other Xaositects.
Xaositects in the World Axis
The Xaositects are actually one of the Planescape factions that made the jump to the World Axis cosmology; as 4e began expanding into the planes, it took up the stance that stuff from Planescape generally happened, at least in broad strokes, with the Great Wheel either not existing or being a now-discredited way of viewing the multiverse that promoted various planar regions to being full-fledged planes. As such, the Faction War happened, amongst other things.
Xaositects were first mentioned in the sourcebook "The Plane Below", which covers both the Elemental Chaos and the Abyss, which introduced the Speakers of Xaos, an offspring sect of the Xaositect belief system and also featured a sidebar noting that it's quite possible that "classic" Axisite Xaositects are still running around; if they are, they have no reason to bug their splinter-group and the Speakers likewise don't give them any second thought.
This would ultimately be expanded upon in Dragon Magazine #414, where the Xaositects made their return as a planar character theme, alongside the Society of Sensation and the Transcendant Order. In the World Axis, Xaositects believe that reality lacks rules and, by extension, any hidden meaning; attempting to impose any kind of structure is antithetical to what it all means, and trying to stem the tide of change and disorder puts you farther away from understanding it all and finding your place in the chaotic sea of reality. The Xaositect philosophy is one of contradiction; Reality is meaningless, but a lack of meaning isn’t a bad thing in and of itself. Abandoning a search for meaning is the surest way to find it. The more your life reflects chaos, the more your life is like the multiverse, and both are sources of endless surprise.
Whether or not this actually any different to the philosophy of AD&D is up for debate.
Mechanically, the 4e Xaositect theme is quite faithful to the powes of earlier versions of the Xaositect. Its bonus power, Babble, lets you curse a victim within 5 squares to be incapable of speaking coherently until they pass a saving throw once per encounter, whilst at level 5, they gain a +2 bonus to Arcana and Bluff checks, and at level 10, they gain +2 to all defenses against opportunity attacks and cannot be surprised whilst they are conscious. They can also take any of three utility powers; Hornung's Deflector (level 2 encounter, causes a ranged attack that hits you to hit a random creature within 3 squares, which might make it hit you after all), The Die Is Cast (level 6, 1/encounter, you can change the result of a D20 by adding +1d10 and then subtracting -1d4 from the result) and Battlefield Shuffle (level 10, 1/day, when you roll initiative, you and all creatures within a close burst 20 must re-roll initiative; you and your allies do so with a +4 bonus, enemies with a -4 penalty).
Speakers of Xaos
The 4th edition sourcebook "The Plane Below", which covers both the Elemental Chaos and the Abyss, introduced a faction called the Speakers of Xaos, a loose and anarchic organization of mystical and scholastic explorers dedicated to studying the Elemental Chaos. Why? Well, it depends on the individual Speaker; the closest thing the organization has to an overarching dictum is the study of chaos and all its potential, but individual members include pure knowledge seekers, those out to understand the secret powers that govern creation itself, and those seeking mastery over elemental beings.
What does this have to do with the Xaositects? Well, a lot of 4e planar lore took the viewpoint that stuff from Planescape happened or existed, at least in broad strokes, it's just the old cosmology wasn't The Truth. As such, the Xaositects did exist in the World Axis version of Sigil, with a slightly different philosophy: the Axisite Xaositects believed that reality is chaotic and can only be mastered by those willing to understand disorder. The Speakers of Xaos evolved from the Xaositects after the Lady of Pain got sick of the factions and told them to pack their shit and get out of her city; some of the more... regimented ex-Xaositects began communicating with the Lyceum Elemental, a minor cabal of sages and researchers fascinated with the theoretical effects the Elemental Chaos had upon events in the material plane. The two groups ultimately merged together, and thus the Speakers of Xaos were born.
The Speakers of Xaos later returned in the "Heroes of the Elemental Chaos" sourcebook, where being a member of the faction was one of the various Paragon Paths offered in the book. A Speaker of Xaos has the level 11 features Xaos Lore and Xaos Action, the level 11 Encounter Attack Elemental Durance, the level 12 Encounter Utility Repel Elements, the level 16 feature Power of Xaos, and the level 20 Daily Attack Elemental Chains.
Xaos Lore: +1 to attack rolls vs. elemental creatures, elementals suffer -1 to saves against your attacks.
Xaos Action: When you spend an action point, if you make an attack dealing cold, fire, lightning or thunder damage before the end of your next turn, you can widen the effect of that attack. For a melee or ranged attack, it hits 1 extra target that is in range. For a burst or blast, its size increases by 1 square.
Power of Xaos: When you inflict cold, fire, lightning or thunder damage, or inflict damage with an elemental attack, reroll any damage dice results of 1; you keep re-rolling until you roll at least a 2.
Elemental Durance: After hitting a target with a cold, fire, lightning or thunder attack, you can, as a free action, invoke this power; it pushes them 1 square and then, if they move before the end of their next turn, it inflicts 3d10 damage of the same type as the attack that it was carried on.
Repel Elements: Creates a close burst 1 zone that lasts until the end of your next turn. Elemental creatures cannot enter this zone (and are pushed out of it if they're in the area of effect when it goes up), and whilst it lasts, you and all allies gain a +2 to armor class and to your Non Armor Defenses against attacks that deal cold, fire, lightning or thunder damage, or which stem from an elemental creature, so long as you are in the zone.
Elemental Chains: After hitting one or more targets with a cold, fire, lightning or thunder attack, you can, as a free action, invoke this power; creatures that were hit with the triggering attack are restrained and take 15 ongoing damage of the triggering damage type (save ends both), whilst creatures that were missed by the triggering attack are immobilized until the end of your next turn.