A bunch of PrCs as feats. This is mostly for classes that don't have very inspiring class features, like most of the early multi-class PrCs.
Player's HandbookArcane Trickster
Prerequisites: Sneak attack +2d6, ability to cast 3rd level arcane spells, ability to cast mage hand as an arcane spell.
Benefit: When you select this feat, choose one arcane spellcasting class that you possess and one class that you possess that grants the sneak attack ability. One half your levels in each stack with your levels in the other to determine your spells known, spells per day, caster level, and sneak attack ability. Both of those classes are considered favored classes for you, in addition to your normal favored classes.
In addition, you can sacrifice a prepared 0th level spell or an unused 0th level spell slot to use any of the following skills at a range of up to 30 feet for a single skill check: Disable Device, Open Lock, or Sleight of Hand.
Special: A wizard can select Arcane Trickster as a wizard bonus feat.
Blackguard [Fighter]
Prerequisites: Level 1 paladin, Power Attack, evil alignment.
Benefit: You regain your paladin class features, regardless of your alignment, and you are no longer bound by your code of conduct. All of your paladin abilities and spells that function against evil instead function against good, and vice versa. You gain the ability to rebuke undead as an evil cleric instead of turning undead as a good cleric. You project an evil aura instead of an aura of good. Finally, your paladin levels grant you the sneak attack ability of a rogue of one half your class level.
You can gain levels in paladin, despite your alignment and even if you have gained levels in other classes since taking your levels in paladin. Paladin is considered a favored class for you, in addition to your normal favored classes.
Special: A fighter can select Blackguard as a fighter bonus feat.
Eldritch Knight [Fighter]
Prerequisites: Ability to cast 3rd level arcane spells, proficiency with all martial weapons.
Benefit: When you select this feat, choose one arcane spellcasting class that you possess and one class that you possess that grants proficiency with all martial weapons. One half your levels in each stack with your levels in the other to determine your spells known, spells per day, and caster level. You can determine your base attack bonus as though up to one half your levels in the arcane spellcasting class were instead in the class that granted martial weapon proficiency, if this would improve your base attack bonus. Both of those classes are considered favored classes for you, in addition to your normal favored classes.
Special: A fighter can select Eldritch Knight as a fighter bonus feat. A wizard can select Eldritch Knight as a wizard bonus feat.
Hierophant Magic
Prerequisites: Ability to cast 7th level or higher divine spells, Knowledge (religion) 15 ranks.
Benefit: You gain one of the Hierophant's special abilities. (In a proper feat conversion, this would be written out properly).
Special: You can select this feat multiple times. Each time, you can select another special ability.
High Arcana
Prerequisites: Ability to cast 7th level or higher arcane spells, knowledge of 5th-level or higher spells from at least five schools, Skill Focus (Spellcraft), Spell Focus in two schools of magic.
Benefit: You gain one of the Archmage's High Arcana abilities. (In a proper feat conversion, this would be written out properly).
Special: You can select this feat multiple times. Each time, you can select another High Arcana. A wizard can select High Arcana as a wizard bonus feat.
Mystic Theurge
Prerequisites: Ability to cast 2nd level arcane spells, ability to cast 2nd level divine spells.
Benefit: When you select this feat, choose one arcane spellcasting class that you possess and one divine spellcasting class that you possess. One half your levels in each stack with your levels in the other to determine your spells known, spells per day, and caster level. Both of those classes are considered favored classes for you, in addition to your normal favored classes.
Special: A wizard can select Mystic Theurge as a wizard bonus feat.
Terrain Mastery
Prerequisites: Endurance, Knowledge (geography) 8 ranks.
Benefit: You gain one of the Horizon Walker's Terrain Mastery abilities. (In a proper feat conversion, this would be written out properly).
Special: You can select this feat multiple times. Each time, you gain another Terrain Mastery.
Planar Terrain Mastery
Prerequisites: Endurance, Terrain Mastery, Knowledge (geography) 13 ranks, Knowledge (the planes) 6 ranks.
Benefit: You gain one of the Horizon Walker's Planar Terrain Mastery abilities. (In a proper feat conversion, this would be written out properly).
Special: You can select this feat multiple times. Each time, you gain another Planar Terrain Mastery.
Expanded Psionics HandbookCerebremancer [Psionic]
Prerequisites: Ability to cast 2nd level arcane spells, ability to manifest 2nd level powers.
Benefit: When you select this feat, choose one arcane spellcasting class that you possess and one manifesting class that you possess. One half your levels in each stack with your levels in the other to determine your spells known, spells per day, caster level, powers known, power points per day, and manifester level. Both of those classes are considered favored classes for you, in addition to your normal favored classes.
Special: A wizard can select Cerebremancer as a wizard bonus feat.
Unlike most psionic feats, this feat is an extraordinary ability, not a supernatural ability.
War Mind [Psionic]
Prerequisites: Ability to manifest powers, ability to rage, nonchaotic alignment.
Benefit: Your psychic warrior levels stack with your barbarian levels to determine your number of daily uses of your rage ability, your barbarian damage reduction ability (even if you don't have it when you gain this feat), your manifester level, and your maximum power level known. Barbarian and psychic warrior are considered favored classes for you, in addition to your normal favored classes. You retain the ability to rage and can gain further barbarian levels even if you become lawful.
In addition, your rage ability no longer limits your ability to use skills, abilities that require patience or concentration, cast spells or activate magic items that require a command word, a spell trigger (such as a wand), or spell completion (such as a scroll) to function, nor their psionic counterparts. While raging, you can still use all of your feats that do not explicitly require you to not be raging.
Special: Unlike most psionic feats, this feat is an extraordinary ability, not a supernatural ability.
Sweeping Strike [Fighter]
Prerequisites: Great Cleave or War Mind.
Benefit: You gain the War Mind's Sweeping Strike ability. (In a proper feat conversion, this would be written out properly).
Special: A fighter can select Sweeping Strike as a fighter bonus feat.
Fist of Zuoken
See Tashalatora from Secrets of Sarlona. Why not, it already exists!
The Mind's Eye (Web)Advanced Construction [Psionic]
Prerequisites: Boost Construct, Craft (any) 9 ranks.
Benefit: You gain the Constructor's Advanced Construction ability. (In a proper feat conversion, this would be written out properly).
In addition, when you create an astral construct, you can give it one additional special ability from any menu that the construct currently has an ability from. This effect stacks with the benefit granted by the Boost Construct feat.
Utility Construct [Psionic]
Prerequisites: Boost Construct, Advanced Construction, Craft (any) 15 ranks.
Benefit: You gain the Constructor's Utility Construct ability. (In a proper feat conversion, this would be written out properly).
In addition, when you create an astral construct, you can give it one additional special ability from any menu that the construct currently has an ability from. This effect stacks with the benefit granted by the Boost Construct and Advanced Construction feats.
Enhanced Construction [Psionic]
Prerequisites: Boost Construct, Advanced Construction, Utility Construct, Craft (any) 18 ranks.
Benefit: You gain the Constructor's Enhanced Construction and Extended Construction abilities. (In a proper feat conversion, this would be written out properly).
Embed Gem [Psionic]
Prerequisites: Psicrystal Affinity, Craft (gemcutting) 8 ranks.
Benefit: You gain an embedded gem, as per the Crystal Master's Embed Gem ability. In addition, you gain the Crystal Master's Psicrystal Synergy ability. (In a proper feat conversion, this would be written out properly).
Special: You can select this feat up to three times. Each time beyond the first, you gain another two embedded gems.
Healing Touch [Psionic]
Prerequisites: Heal 9 ranks, manifester level 5th.
Benefit: You gain the Sangehirn's Healing Touch ability. (In a proper feat conversion, this would be written out properly).
In addition, you permanently gain the benefit of the biofeedback power, augmented to a number of power points equal to one half your manifester level. You can suppress or resume this effect as a free action.
Psychic Theurge [Psionic]
Prerequisites: Ability to cast 2nd level divine spells, ability to manifest 2nd level powers.
Benefit: When you select this feat, choose one divine spellcasting class that you possess and one manifesting class that you possess. One half your levels in each stack with your levels in the other to determine your spells known, spells per day, caster level, powers known, power points per day, and manifester level. Both of those classes are considered favored classes for you, in addition to your normal favored classes.
Special: Unlike most psionic feats, this feat is an extraordinary ability, not a supernatural ability.
OtherMind Arrow [Psionic]
Prerequisites: Throw mind blade class feature, Point Blank Shot.
Benefit: You gain the Soulbow's Mind Arrow ability, minus the references to gaining enhancement bonuses to your mind arrows and your soulknife base attack bonus. (In a proper feat conversion, this would be written out properly).
Special: Unlike most psionic feats, this feat is an extraordinary ability, not a supernatural ability.