First up, a quick redux of Weapon Focus I created for the Request a Homebrew thread:

Weapon Focus
Benefits: When you take this feat, choose one of the following weapon groups: light blades; heavy blades; flails and chains; spears, staves, and polearms; bows and crossbows; hammers and maces; axes and picks; or slings and polearms. You gain a +1 to attack rolls with all weapons in that group.
Spoiler: Group Lists

Light Blades: dagger, punching dagger, sickle, kukri, shortsword, rapier, kama, sai.
Heavy Blades: longsword, scimitar, greatsword, scythe, falchion, bastard sword, two-bladed sword.
Flails and Chains: flail, heavy flail, dire flail, spiked chain, whips.
Spears, Staves, and Polearms: shortspear, spear, longspear, trident, quarterstaff, glaive, guisarme, halberd, lance, ranseur, dwarven urgrosh.
Bows and Crossbows: shortbows, longbows, composite shortbows, composite longbows, light crossbow, heavy crossbow, hand crossbow, repetaing heavy crossbow, repeating light crossbow.
Hammers and Maces: light mace, club, heavy mace, morningstar, light hammer, greatclub, warhammer, gnome hooked hammer.
Axes and Picks: throwing axe, handaxe, light pick, battleaxe, heavy pick, greataxe, dwarven waraxe, orc double axe, dwarven urgrosh.
Slings and Thrown Weapons: slings, dagger, club, shortspear, dart, javelin, spear, throwing axe, light hammer, trident, sai, bolas, net, shuriken.

In addition, you gain a special benefit when wielding a weapon of the type you chose. The benefit only applies to that weapon, not any others you might also be holding.
  • Light Blades: You may add your Dexterity modifier to damage.
  • Heavy Blades: You can use the handguard (or handle in the case of the scythe) to guard against attacks, gaining a +1 bonus to shield AC. This ability stacks with other shield bonuses, including Two Weapon Defense and actual shields.
  • Flails and Chains: By wrapping the chain around an opponent's throat, you may use this weapon in a grapple with no penalty.
  • Spears, Staves, and Polearms: If the weapon has reach, you may switch your grip on it as a swift action to lose reach, but gain the ability to attack adjacent foes. If it does not have reach, you may switch your grip as a swift action to gain it, but lose the ability to attack adjacent foes with it as usual.
  • Bows and crossbows: You no longer provoke attacks of opportunity for firing your weapon.
  • Hammers and Maces: On a successful critical hit, the enemy must make a Fortitude save (DC 10 + your Strength mod) or be knocked prone. Bonuses against being tripped can be applied to this save.
  • Axes and Picks: On a successful critical hit, the enemy continues taking damage each round equal to your Strength modifier. This damage can be stopped with a DC 15 Heal check or a single point of magical healing.
  • Slings and Thrown Weapons: You can reload/draw these weapons as a free action, if you could not already. In addition, increase the range increment of each weapon by +20 feet.

Special: You may take this feat multiple times. Each time you do, it applies to a different weapon group.

Fighters may take this feat as a fighter bonus feat.

Spoiler: Thoughts
Since this was created as a request, I don't personally use this feat myself; however, I might do so if I were to run a game with newer players, as my Interesting Weapons project is a little bit complex.

I didn't expand upon this feat any further up the chain (Weapon Specialization et al) in the thread, but at the very least I'd say they all apply to a chosen weapon group instead of a single weapon. Could be used with Unearthed Arcana's weapon group proficiency system, but for the fact that I altered the group to be based more on weapon design than typical users (ie no "Druid Weapons" group).