Tremorsense (Ex): Level 3. Distance is +60 feet each time this ability is taken.
So, after level 3, you can take this feat as often as you like? Awesome! I just have to take it 88 times and I'll be able to locate anything touching solid material within a mile of me.

Battle Spirit (Ex): This feat grants two stances, either of which is active as long as the character is conscious and spends a Swift action each round.
Calm Stance: Gain +1 Competence bonus to AC, Reflex saves, Spot and Listen checks for every 5 levels (levels 1, 6, 11, and 16).
Rage Stance: Gain +2 Competence bonus to attacks and damage, and +2 Damage Reduction (no weakness, or add to pre-existing DR), for every 5 levels.
Any swift action, or a swift action to maintain the stance? If either can be active at any time, with no activating action, does that mean a character with this feat can be in Rage Stance during attacks, then immediately switch to Calm Stance for the rest of the turn?
Fast Healing (Ex): Level 3, Constitution 19+. Heal 1 HP at the end of every 10 rounds. At level 6 increase the healing to 1 HP every round. Gaining this ability again increases the healing amount by 1 each time.
Regeneration (Ex): Level 8, Fast Healing 3, Constitution 23+. Convert all damage to nonlethal except from fire or acid. Limbs may be reattached or grow back after 3d6 minutes.
Do you still lose the fast healing effect once you take regeneration, as in core?
Stunning Strike (Ex): DEX 13+ or WIS 13+. By spending a Swift Action, until the end of the round each critical hit confirmed within 60 feet may cause Stun to the target for no more than 1 round. The Swift action may be spent after attack roll is made.
Any confirmed critical within 60ft of
you or the target? Is the range on this unlimited or does the critical have to come from you, specifically?
Cleave (Ex): STR 13+. Whenever one of your melee attack actions hit you may spend a Swift action to attack again.
I'd call this Double Attack rather than Cleave, unless you intend that the extra attack can be made against any target in reach
except the one you hit.
Weapon Specialization (Ex): BAB 4+. For a single attack in each round all damage for one type of weapon is maximized.
Greater Weapon Specialization (Ex): BAB 12+. All damage for one type of weapon is maximized.
By type do you mean handedness (light/1-handed/2-handed), complexity (simple/martial/exotic), damage type (bludgeoning/piercing/slashing), or something else?
Lunge (Ex): STR 15+ or DEX 15+. BAB 6+. The character's natural reach becomes equal to half their land movement distance. They may take the space of any location within reach as part of an attack action.
Permanently!?! That can be a whole lot of reach with enough movement speed enhancements.
Hide in Plain Sight (Su): Hide 15 ranks. By spending a Swift action, the character may gain total concealment and become Invisible as the spell for 1 round, as long as no aggressive action is made.
Invisibility at will. Fun! Now you never again need bother with that pesky Hide skill you just sunk 15 points into... Please tell me that sounds as silly to you as it does me.

Impale (Ex): Each time a critical is scored with a Piercing weapon the target is Slowed until they spend a Move action and lose 5 HP, removing the impaling weapon. The Piercing weapon may not be used while Slow condition is applied to the target in this way but may be regained at the end of the round once the weapon is removed.
So the target is slowed on its next move action and loses 5 more hp, but you can't use your piercing weapon for deflect, block, cleave, master strike, or any of the other wonderful swift-action-using feats you've created until they do so? Seems like a bad deal to me.
Sneak Attack (Ex): DEX 13+ or INT 13+. Whenever an opponent denied their Dodge bonus is hit with an attack within 60 feat you may add 1d6 Precision damage. Taking this ability again increases the Precision damage by 3 each time. This ability may not be taken more than once every odd level.
I like this change. One of my more commonly used house rules is that all damage is static (dice are maximized, then halved), but the player can choose to subtract damage from the total and roll 1d6s instead at a rate of 3 per, up to half the original damage. (This way "Maximized" always effectively equals +50% damage)
Mobility (Ex): DEX 13+. Each time the character takes a move action they gain +4 Dodge bonus to AC until the beginning of the next round.
So if I take two move actions in a round I gain a +8 Dodge bonus to AC, right? (since dodge bonuses stack)
Flashstep (Ex): DEX 13+, BAB 5+. The character may make a Move action as an Immediate Action, but lose the next Move action or 5-foot step they would be allowed to make later in the same round.
So with this I trade a 5-foot step or move action
and a swift action for an
immediate move action? Kinda situational, but I like it.
Wraith Strike (Su): WIS 13+ or CHA 13+, BAB 7+. By spending a Swift action the next attack made ignores armor bonuses. The Swift action may be spent after attack roll is made.
Unseen Strike (Ex): STR 13+ or DEX 13+, BAB 5+. By spending a Swift action the next attack made ignores Dodge bonuses. The Swift action may be spent after attack roll is made. This does not make the target flat footed.
So, if I had the feats, I could spend several swift actions three weeks or more in advance to have a
Perfect Unseen Cleaving Wraith Strike at the beginning of my next combat?
Improved Flashstep (Ex): DEX 15+, BAB 10+. The character may make a Move action and a single attack as an Immediate Action, but lose the next Move action or 5-foot step they would be allowed to make later in the same round.
Now we're talking! Trade a 5-foot step or move action
and a swift action for an
immediate move and attack action. This will definitely come out ahead in most situations. Only slightly less versatile than your Quickness feat, though it has steeper requirements.
Improved Action (Ex): The character gains +1 Swift action in a round for every 5 levels (1, 6, 11, and 16). Spending 2 Swift actions allows a reroll on a failed save, while spending 3 Swift actions allows a reroll on a failed attack.
Wicked! Now I can potentially make a
Deadly Perfect Unseen Kinetic Whirlwind Cleaving Wraith Strike at the beginning of any combat! By level 11 even, provided I crit! Combine with Lunge, Power Attack (that's 10/12 feats so far) and some speed enhancements to one-shot entire armies as you leap across them,
exploding mid air.

Antimagic (Ex):
BAB 1+: +2 Resistance bonus to all saves against magic
BAB 6+: +5 Resistance bonus to all saves against magic
BAB 11+: +10 Resistance bonus to all saves against magic
BAB 16+: constant Antimagic Field effect with a range of Self (can be suppressed)
Does this count as spell resistance for the purposes of your Deflect and Improved Deflect feats? I'd
love to be able to play baseball with lightening orbs!

Also, do you intend that characters be able to combine Mobility, Quickness and Improved Flashstep and thus regularly move at 6x speed with a +12 Dodge bonus to AC and still make an attack action? If so, you have made a thing of beauty.