Offensive Tractoring
Gravity wave focusing enables the long-range gravitational tethering of ships. The tech line is designed to enable beam-warships to trap and tether ships outside the combat range, slowing them in much the same way that a black hole interacts with non-newtonian technology.
The technology could also be used by missile ships to play "keep away" on beam ships-- shaving their precious speed advantages.
Example: A class 1 offensive tractor would slow the target ship by 1000 km/s.
Range would have to be considered. I was thinking the 20-50 m/km range to give beam ships a middling way to project power over long ranges.
Power Requirements: I'm thinking these babies should be a huge draw on power. This would prevent people from plopping a class 10 megatractor on every ship in the fleet-- you need a big heavy tractor, plus a big heavy powerplant to run the thing continuously. No capacitors, because the weapon needs a continuous power supply.
Finally, you know you want this, because
BOARDING OPERATIONS
Nuff said.