If you want a quick and dirty system, take the FATE one. Each skill, ability or whatever has a rating
When you roll the dice, you roll 4 d6s.
Giving you a possible -4 to +4 variation. Add that result to the skill / ability rating, and there is your final result for the action.
You also have aspects, which are special triggers that give a +2 bonus. For example, I might have a Street Samurai with an aspect of My Lucky Gun. When I use that particular gun, I get a +2. Alternately I might have an aspect of I Know A Guy ... so when I'm doing rolls for Investigation, or Contacts , I could invoke that to get a bonus. In FATE they're invoked with the use of Fate points, of which you have a limited but refreshable pool.
Thats about as simple as a quick and dirty system as I can think to give you.
Having lists of equipment is handy, but as you've said, it's freeform. Is there really going to be any difference in your freeform AK-97 assault rifle and your freeform HK-223? Put in a wiki for general groups of equipment, maybe toss in some specific examples, and then let the players go with what they want. If you want equipment to matter, give it a quality rating. Poor quality is a -1 (but its lots cheaper), average is 0, good is a +1 (but more expensive).
Work out skill groups perhaps, and let the players put points into those. Specialisation gives me a bonus to a subgroup, but costs another point. I'm Fair with Firearms, Good with the Rifles , and Great with Sniper rifles. With my Custom Sniper Rifle I'm Fantastic. Of course, with all those points in there, I'm probably not so great with many other skills, but that's what happens when you specialise.
Does that give any food for thought?