No it is not a drive or a weapon though the title suggests some really neat drives and weapons. It deals with a modification to your 2d6 system of choice. Invert the rate at which you use fuel in space craft.
So in most systems that means you burn .01 of the ship's 'mass' in fuel * p-ower plant number per month using the jump drive. That extends the range of a ship by four, assuming a basic load of fuel. there isn't a captain living that wouldn't jump at that deal but there is more.
A straight interpretation of inversion means your maneuver drive now uses .1 of the ship's mass per drive number. I assume that would be for one week under thrust. A ship that could thrust at one gee for one month would have to be 40% fuel! A ship with a thrust of six gees would need 60% fuel to thrust for a week and could only manage 1.5 gees for an entire month.
Accelerating for 1 gee for a week (accelerate, flip, decelerate) will take you 900 million miles or about 8 AUs. Almost to Saturn. Why you want to go that far in a Traveller style system is up to your referee (who is no doubt reading this and plotting). You can also just make a jump in system that far or longer for much less fuel.
With the fuel inversion of course you could just jump into a system and jump right away to another without all that pesky refueling. defenses in depth will need much more depth. If you allow jumps to and from 'empty' hexes it will play hell with canon ideas of defense.
The idea has appeal for merchants. A mainworld has an average diameter of 8,000 kilometers. That's a mere four hours away at one gee, your M-drive fuel, even a mere 10% would last you 33 such trips on average! Note that a 200 ton ship uses 20 tons of fuel for a jump of one parsec in the old system. That's 10,000 credits twice a month (on average) except now that ten tons will last about seven months (four in system hops a month 5 hours each). The fuel for the j-drive will come to 7,000 credits in seven months (two ton a month). Using the CE rules that ship will on average burn 48 tons a month and in seven months pay 168,000 cr. So fuel costs are a real factor even with a mortgaged ship. A 200 ton trader'r mortgage runs 35 Mcr. The mortgage is 146,000 cr. The mortgage is less than the fuel costs ('not even going into the life support, maintenance, berthing, and salaries -you know that I could.)
So fuel inversion makes defense a lot harder, exploration and invasions a lot easier and it reduces the monthly costs of your plain old trader by half. The merchants still have to scramble for credits somewhat but it isn't quite as frantic a pace, meaning they have more time for adventuring. Ships that have to make even short inner system runs might not use their thrusters. The jump drive is far more fuel efficient. They would if time were a factor and they were getting supplies from the same system. An orbital port might be at the jump limit, accepting cargo from ships and launching it to the destination with a magnetic accelerator to save on fuel.
One more thing, the fuel inversion effect avoids the gig of global destruction problem. No ship will carry enough fuel/propellant to reach anything close to light speed. Just accelerating at one gee for a week gives you 6048 kps. That's fast but not impossible to stop or survive.
Of course that accelerate for a week business is from a literal interpretation of 'inverse'. People may want less acceleration time. You could go with 10% of the ship allowing a day or an hour at one gee. In that case you're down to insisted traffic taking weeks if not months and anything beyond far orbit will probably see the use of jump drives.