I think rapid fireing  pulse phasers

you can make them fire 3 shot burts yourself, by using the save-fire feature used by some of the torpedoes  works well for me in V2.  

look at the excelsior torpedo odf (found in odfs >weapons >torpedoes  (see how that works   )) you should see these 3 lines at the bottom:

saveFire = 1
maxShots = 3
minimumShotInterval = 0.5

now providing you have left a big enough time delay between shots it will fire 3 shots if it hasn't attacked in a while. this can be done to most pulse weapons that i came across ie. defiant pulse, (as well as every torp)