UnderBarrel: Extended Barrel: Keeps damage at longer range. Reduced mobility.
Sawed off: Bullets go faster, slight damage increase, less range more recoil.
Under barrel: Smokethrower: Sort of like a flame thrower, when you equip it and shoot it sprayes a area of smoke like paint where ever you point it. So, you can make a ring of smoke around you, or a small wall of black smoke. Slower relaod. Would be best if you decided to use the slot for smoke grenades for something else.
Trip Wire: You have two shots, and they only work at a certain range and if they hit a wall. So, basiaclly you shoot two parralel walls with this thing that ressembles a grenade launcher. If they walk itno it, they stumble and the camera fubles around, but they can still shoot. If they sprint they trip onto their shins, they can't shoot, and if they are in mid Smart move they trip and do a roll. All of they take barely anytime, so it looks smooth as the person is delayed but not really stoped. And, you can't make the wire really long, I think the max should be a medium street. Reduced mobility.
Flashlight: If your crossairs are pointed at the top of their torso/head they are slightly blinded. Maybe there should be a general ability called sun galsses. Longer to take out.
Rail: I found this to be the most boring slot, so I tried to think of unique things ou could do with it.
Night vision red dot sights/scopes
Booster sight: This is a very strange thing I have thought up as, I thought it was a real team player sort of thing to have basically it's a red dot sight with various calculations going one when you look thorugh it to give it a future like feel. When you aim at a friends, a bar comes up. It takes you 3 secondes to "mark" them (That is actually quite a while if you think about it) When they are marked they get a slight general boost, so half a pip, they more a bit faster, and do -berely- a bit more damage. You can do it only once per life and it lasts 10 seconds. More recoil, less damage.
The stalker: The opposit. Say you see a light operative sneaking around, makin mischeif, but you can't really hit him. While you aim, a bar comes up, and if it takes 1.5 seconds to fill, the guy is marked in a different way: for 10 seconds a red dot appears on the main screen where ever he is, even if he is behind walls, so you can find him. You are alerted when you are marked, there should be a operative ability that cuts marked time in half. Same cons as the booster.
Magazine/bottom:
Quick switch mags: You gun is modded so it has two mag wells, but only one works. So, when you relaod, you drop the first mag, and REALLY fast take out the other mag next to it and put it in the real one, so you berelt have to reload, great for when you are about to go into battly. The bad part is the relaod time is double because you have to put two in.
I have many more I can't remember, and I might post my favorite ones you guys come up with. I'd quite like to see what H0rse comes up with.
OH AND BY THE WAY, please son't confirm anything or talk about confirmed ones, I want the majority of them to be a suprise.