Many of the core and base classes of Pathfinder have different roles in Devaia than they do in other Pathfinder games.
In Devaia, Paladin and Anti-Paladin are the only core and base classes that possess alignment restrictions.
Devaia is a world caught in the throes of scientific and magical revolution, and alchemists are very good at advancing both fields. Alchemists are very often on the cutting edge of innovation, and they fulfill a very important role in Devaia.
Although many barbarians come from primitive tribes, not all do. Their rage ability and durability makes them useful shock troops, and many militaries specifically train people for such roles. Therefore, many barbarians come from more civilized roots.
Some barbarians focus on ranged combat, and gain a dexterity bonus instead of a strength bonus while raging. This is an alternate class feature available to all barbarians in Devaia, but not major enough to be an archetype.
Bards in Devaia fulfill much the same role as bards do in almost all Pathfinder games. Their place in the world is one that transcends societies and technology levels.
The gods of Devaia do not show themselves. The fact that divine magic works and the existance of outsiders and alternate planes of existance is often, though by no means always, taken as proof of their existance, but the debate as to what they wish from their followers and even as to which dieties exist is endless. The fact that corrupt clerics do lot lose their powers further complicates this. Aside from the uncertainty of religion in Devaia clerics fulfill much the same roles as in any other Pathfinder game.
Throughout most of history, divine magic has been seen as the only pure and acceptable magic, and arcane magic, mostly in the form of witchcraft, as something not to be trusted. Clerics served on the front lines of this war against arcane magic and it's users, and only within the last several decades has the war cooled down. Many clerics, however, are still vehemently opposed to arcane magic.
Druids in Devaia are stalwart guardians of nature, but they are not necessarily opposed to civilization or technology. While some certainly do loath both of these things, others are accepting of them, believing that nature and technology can coexist if people are willing to make an effort to be responsible with technology. While these druids will not tolerate that which brings unneccesary harm to nature, they are otherwise pro-technology, and many make full use of it.
Fighters in Devaia are professional soldiers, sailors, pilots, and drivers. They are very similar to fighters in other Pathfinder campaign settings, but lack the armor training and armor mastery abilities do to the inavailability of armor. At any level when they would gain one of these abilities, they add 5 to their hit points gained for that level.
Everybody in Devaia has guns, but gunslingers make their use into an art via the grit mechanic. They may not be the most professional warriors around, but their style is undeniable.
<Devnote: The gunslinger needs some new abilities to replace some features that are common to all characters in Devaia. Dev personally recommends this.>
Inquisitors in Devaia fulfill much the same role as inquisitors in other Pathfinder games, and the uncertainy of religion and the precise will of their diety makes Devaian inquisitors rather dangerous. Few good aligned people will kill and torture for a diety thy can't even prove exists. Though they can be good aligned hunters of threats of divine origin and corrupt clerics, they are more often brutal and tyrannical enforcers of a corrupt and greedy religious order. Like clerics, corrupt inquisitors do not lose their powers.
Historically, inquisitors have served alongside clerics on the frontlines of the war on witchcraft, and although arcane magic is becoming more acceptable, some inquisitors, just like some clerics, still cling to the old ways.
The magus is somewhat melee focused, which doesn't fit Devaia well. The best option for a character who wants to play one is to take the gun mage alternate class linked to here, which is a well designed ranged magus. The idea of a gun magic is not unheard of in Devaia, and is in fact a rather popular pursuit for more martial oriented students of magic.
Monks certainly exist in Devaia, but they are rarely adventurers. They mostly keep to their studies. Those that are adventurers are mostly Zen Shooters, as using unarmed combat techniques against somebody with a gun rarely ends well. A Zen Shooter is an archetype that is identical to the Zen Archer, except all it's abilities apply to guns instead of bows. Zen Archery gives wisdom to both attack and damage in place of dexterity. The wisdom bonus to damage is 1 1/2 times wisdom for two handed firearms and haf wisdom for off hand firearms, just like dexterity.
Most oracles in Devaia struggle to understand what dieties chose them and why, but otherwise function much like clerics, often but not always with a divination focus.
Paladins in Devaia are usually either in direct service to a church or government or rebels. Unlike other divine spellcasters, a paladin who becomes corrupt does lose class features as per the rules in the CRB. This is because of the intrinsic goodness of paladins, which cannot exist in harmony with corruption. Paladins may not be perfect, and they do not fall for every mistake they make, but they must remain champions of good at all times if they wish to remain paladins.
Rangers serve a great many roles in Devaia. Some are guardians of nature, some are scouts, some are explorers, some are archaeologists, some are hunters, and some undertake other roles I haven't thought of. They are an incredibly diverse bunch, with only their wilderness and combat skills linking them together.
Rogues in Devaia fill the same roles as in any other Pathfinder game. Their place in the world is one that transcends societies and technology levels.
Sorcerers have always existed in Devaia, though the utility of their powers was somewhat limited until around 50 years ago, and do to the frequent witch hunts which failed to distinguish between witch and sorcerer they mostly stayed hidden. This has all changed with the growing usefulness of arcane magic and the end of large scale witch hunts, and sorcerers are finding themselves both more powerful and more socially accepted. Since sorcerers have historically been much less powerful than they are in the modern day, there is little in the way of past knowledge or community for them to turn to in order to help understand their powers. Most are on their own in this regard.
For hundreds of years witches have been the most common arcane spellcasters in Devaia. Due to the long casting times of spells up until around 50 years ago, the effects witches produced, which do not require rapid casting to be effective, were the most useful of all arcane magics. However, being the only arcane spellcasters around aside from the occassional sorcerer had it's drawbacks. Arcane magic was seen as something not to be trusted and divine magic as more pure, a belief only now fading away, and therefore witch hunts were highly common. Do to this mistrust, witches have always been a rather secretive lot, careful not to tell outsiders of their ways.
Unlike in other Pathfinder games, witches in Devaia do not gain their powers from familiars. They gain it from study, just like wizards. Witches differ from wizards in being an older and more secretive tradition and having hundreds of years of knowledge to fall back on that wizards lack. Witches have a choice between summoning a familiar and forming an arcane bond. Witch familiars in Devaia work the same as wizard familiars, as does the arcane bond feature. A witch writes spells in a grimoire, which functions like a wizard's spellbook but holds a great deal of ritual signifigance to the witch. A witch who loses a grimoire is treated as a witch in another Pathfinder game who has lost a familiar. A witch coven does not need to posses a hag. Add bluff to the witch class skills.
Wizardry is a very young art in Devaia. Up until around 50 years ago, arcane magic simply took too long to cast for any type other than witchcraft to be practical. That all changed with the discovery of different casting methods that made casting quickly feasible, allowing the study of wizardry to suddenly have a practical use. The study of wizardry is in it's infancy, and wizards are still figuring out what is and isn't possible. There is very little old knowledge to fall back on, as wizardry is only about five decades old, so innovation is key.
<Devnote: Not all classes available in Devaia have been added to this list.>