Weapons

Muzzle Attachments

 * Choke: Tightens the pellet spread of shotguns. Can be attached to shotguns only.
 * Compensator: Generally reduces recoil. Separate versions for SMG's, Assault Rifles and Sniper Rifles.
 * Flash Hider: Hides the muzzle flash and makes it quite a bit harder to figure out where you're shooting from. Separate versions for SMG's, Assault Rifles and Sniper Rifles.
 * Suppressor: Hides the muzzle flash and suppresses the sound, thus making it very hard to figure out where you're shooting from. Separate versions for SMG's, Assault Rifles and Sniper Rifles.

Magazines

 * Extended Magazine: Increases the amount of ammo your magazine can hold by either, 12, 10 or 5, depending on the weapon you're using. Separate versions for SMG's, Assault Rifles and Sniper Rifles.

Grips

 * Triangular Grip: Reduces the horizontal swaying of some guns. Can be attached to almost all weapons.
 * Vertical Grip: Reduces the vertical recoil. Can be attached to almost all weapons.
 * A video of AR weapons with different grips attached

Scopes

 * Red Dot / Holographic: Doesn't zoom in at all, thus making it very useful for indoor and short-range combat. Which one you want to use is up to you, personally I prefer the Red Dot since its frame is slimmer. Can be attached to almost all weapons.
 * 2x: Zooms in by 2 times, useful for short to mid-range combat. Can be attached to almost all weapons.
 * 4x: Zooms in by 4 times, useful for mid to long-range combat. Can be attached to almost all weapons.
 * 8x: Zooms in by 8 times, useful for long-range combat. Can be attached to almost all weapons