this gun would shoot small aliens away from the human when hit!! this gun would spray pulses that damage and propel aliens the size of adv mara and under back! this would be use of secondary gun! still deals damage to aliens like goon and rant tho!
In fact, the Lighting Gun is already a weapon from Quake 3 which Tremulous is based off of. Perhaps this is something that can be trivial to actually have in-game. 
New Edge already ported the lightning gun to trem, although it works differently from what sun described.
mmm tesla gun? like RTCW tesla?
so go grab code from rtcw sp or mp (it too idtech3, GPL2 and etc)
and adapatate it to trem 
P.S Rtcw have only code GPL2, use RTCW resources in trem - JHON KARMACK WILL FUCK YOU!