A recently discovered "black hole" grenade whose explosion will create a black hole vortex. Is first thrown and then activated by a second attack press, like a remote mine.
While not in any currently released Valve product, this weapon can be enabled (possibly in ep1 only) by entering the following into the console:
It is currently speculated that this weapon will be recieved by Gordon Freeman in Episode 2.
http://www.halflife2.net/forums/showthread.php?t=110926 - Forum thread about the grenade.
http://www.joystiq.com/2006/08/06/the-hl2-episode-1-black-hole-grenade/ - Article with movie.