In terms of raw "power" the Dark Matter Gun is without a doubt the most formidable of the Strogg infantry weapons. Presumably more experimental than the Lightning Gun, the Dark Matter Gun is capable of clearing entire rooms of hostiles with a single blast, similar in operation to the BFG10K. The Dark Matter Gun projectile reacts with its environment, the result being an impressive explosion which wrenches apart the fabric of any nearby organisms. Slow to fire and reload, the Gun makes for a perfect way to "soften" up a room prior to assault.
Despite the name, this technology appears to have little to do with actual cosmological dark matter.
in quake wars there is a dark matter cannon