Slash'em is a clone of the text based adventuring game NetHack.
It stands for Super Lotsa Stuff Added Hack - Extended Magic
Nethack: From the land before 3DFX, before VGA graphics and DOOM, before the IBM PC, way back in the dark ages of Unixland, there was a game. They called it Rogue. People played it, and found it good. From this basis, Hack was born. Soon Hack became Nethack, because it was developed by many people (and has nothing to do with hacking the internet). And people played this on many machines, from Unices to Macs to PCs, due to the amazing power of Open Source Code.
But the DevTeam, the reclusive masterminds of Nethack, are a rather quiet bunch, gracing the world with new versions as they see fit, and when they see fit. Which is usually a new version every good number of years.
And there was much gnashing of teeth.
But because of the Freely Available Source Code Phenomenon, people began making their own versions of Nethack to tide themselves between magical releases.