The Strange Aeons adventure path has a number of interesting campaign traits, some of which are quiet useful.
Driven by Guilt:
You gain a +1 trait bonus on saving throws against any spells or spell-like abilities cast by evil creatures. In addition, once per day as a swift action, you can add your Charisma bonus to your attack rolls and deal 1 additional point of damage for each class level you have against evil creatures for 1 round. You must have a good alignment to take this trait.
Enduring Stoicism:
You gain a +2 trait bonus on all saving throws against spells or effects with the fear or emotion descriptors. In addition, you gain a +1 trait bonus on Intimidate checks due to your intimidating presence, as people don’t know what to expect from you.
Foe of the Strange
You gain a +1 trait bonus on saving throws against extraordinary, spell-like, and supernatural abilities of aberrations (for example, a gibbering mouther’s gibbering or an intellect devourer’s confusion). In addition, whenever you’re confused and roll to determine behavior in a given round, subtract 10 from the result.
Formerly Mindswapped:
Once per day, you can reroll one Knowledge check that you have just failed. In addition, you can attempt untrained Knowledge checks with DCs up to 20 instead of 10.
Methodical Mind:
Choose three Knowledge skills. You gain a +1 trait bonus on Knowledge checks of these kinds and on concentration checks. In addition, choose one Knowledge skill. When researching, you are considered to have Skill Focus for that Knowledge skill when determining what die you roll to reduce a library’s knowledge points (kp).
Pugnacious:
You gain a +1 trait bonus on attack rolls when threatened by two or more enemies. In addition, once per day you can gain one of the following effects as an immediate action: You can increase the reach of your melee attacks by 5 feet for 1 round, or you can treat your weapon as one size category larger than it actually is for purposes of determining damage for 1 round.
Ritualistic:
Choose one 0-level spell. You can cast this spell once per day as a spell-like ability with a caster level equal to your character level. The spell-like ability’s save DC is 10 Charisma-based. In addition, you gain a +2 trait bonus on all skill checks when performing occult rituals.
Sensitive Mind:
You gain a +1 trait bonus on Appraise, Perception, and Sense Motive checks, and one of these (your choice) is a class skill for you. In addition, once per week you can use the psychometry occult skill unlock even if you are not capable of casting psychic spells or have the Psychic Sensitivity feat.
True Devotion:
Once per day when casting a divine spell, you can attempt to cast the spell without losing the spell from its spell slot or using one of your allotted spells per day. There is a 20% chance that this attempt is successful.
In addition, select one domain or inquisition you have. You can use the first granted power of that domain or inquisition one additional time per day. You must have a good alignment and be class capable of casting divine spells in order to select this trait.
Twitchy:
You gain a +2 trait bonus on initiative checks and a +1 trait bonus on Reflex saves.
Former Mindswapped in particular is pretty interesting, given the boost to untrained knowledges. I know there's some untrained skill builds floating around that might benefit from that.
Pugnacious meanwhile is just straight up gravy for a melee combatant.
Inner Sea Intrigue has a number of interesting rules- from being a comicbook superhero (or villain)- to spreading rumors- to additional stylized spell stuff (via a 'greater' feat). Most of the stylized spell options are 'pick a trait of the spell, the spell appears to have a different one- so stuff like 'descriptor' 'type (ray/burst/whatever)' 'origin point' (entirely cosmetic but potentially useful).
But down at the end there's an option for suppressing the visual or auditory effects of a spell. Enemies can make a perception check vs (10 + highest of either bluff or spellcraft ranks + highest of your mental ability modifiers)- if they succeed they notice the suppressed effects, but if they fail they basically don't see or hear anything.
So yes, you could make an invisible fireball with this. Or nearly so.
Some new Inquisitor domains. One lets you go invisible a number of times per day, with a decent duration. My favourite, though, is the Seduction Inquisition. Granted powers are a hoot. The first lets you basically flirt with someone. Charisma check vs a piss easy DC (10 + the target's wis mod) if successful they let you talk with them for a minute when they wouldn't otherwise. Useful on guards and prisoners or the like. You can use it in combat to feint, too!
The second though, is where it's at. By fucking for an hour ("engaging in acts of physical pleasure with a willing partner") you can use a diplomacy check to improve that partner's attitude, improve your influence with them, or decrease a rival's influence with them,
with no maximum on the number of steps by which you change that disposition.
There's an investigator archetype based around getting a familiar, and that familiar using your class features. Also picks up improved familiar later on. There's an alchemist archetype that works similarly, except the familiar you pick is actually clockwork, and gets improved familiar later (but clockwork) and some other stuff.
Various gear of note- ranging from poison antidotes to the glider staves from Avatar.
There's a +2 magic weapon effect called Obliviating. This does basically what you think it would do. It only works on a bludgeoning weapon, but when you crit
or deal sneak attack damage to a target, they have to make a DC 16 fort save or lose all memory of the past 1d6 minutes (and become flat footed until the start of their next turn).
There's a +1 weapon effect called training that grants one combat feat while the weapon is held/wielded. The feat can't be used for prereqs, and you have to meet its prereqs to use it, but it's still effectively a free feat.
There's a hat of infinite disguises, costing 12,500 gp which uses Veil, rather than disguise/alter self.
There's a 7th level spell that lets a target wear a corpse as a meat suit. Ever wanted to impersonate the king? Now you can.
Various other stuff, but I'm not familiar enough with the classes to say if they're useful or not.
