The Bowcaster appeared to be something like a black cross bow, however, instead of firing arrows, energy particles fired out of the tip. The energy was coloured green. The weapon also appeared to be two handed, with one hand handling the trigger while the other was left free to level the Bowcaster at the target the Wookiee was aiming at.
 In Star Wars: Battlefront
The Bowcaster was the primary weapon used by the Wookiees, and could be powered up for a single blast capable of killing another unit or fired in a spread fashion. Wookiees also made use of grenade launchers in that game.
 In Star Wars: Knights of the Old Republic
Chuundar and Zalbaar both had their own modification capable Bowcasters which could be wielded by any character with the correct training. A number of other Bowcasters could be obtained. While a capable weapon, it is not the most powerful and often other weapons were used in it's stead.
 In the Movies
In a number of scenes in the prequels, you can see wookiees making use of their bowcasters against the forces of the CIS.