According to a .sig on rec.games.roguelike.angband, it's a game where "an '@' sign runs around slaying letters in search of punctuation."
Notable examples of this type of game include:
I don't know if I agree with DiabloIi being a RoguelikeGame. I think one of the qualities of a RoguelikeGame is that is is text based with monsters and items etc being represented by single characters. DiabloIi being graphical would not qualify. -- BenZeckel
Many RoguelikeGames these days also support graphical tiles in addition to the original text-based "graphics". A couple are completely graphical. DiabloIi really pushes the boundary of "roguelike" more because (a) it's real-time (whether the now-defunct Utumno would've been considered roguelike is anybody's guess) and (b) it doesn't involve any actual tiles. Also, by and large, the gameplay seems to aspire to that of Gauntlet rather than AngBand. It does have definite roguelike tendencies, and anyhow it's fun...
Omega lets you generate yourself as a character -- just answer the questions to find out your stats.
Where else can you get messages such as 'There is a well-made repeating kill-o-zap gun (12 ammo remaining) here'?
Uh, Boss (a Moria variant), probably -- most of the item renames are just for flavor (scrolls -> floppy disks, wands -> ray guns) but there are also handguns of various sorts (though this is one of the translations that doesn't work well... seems kind of silly to pick your bullets up off the floor when you miss...). Admittedly, Boss didn't let you do severe damage to your hands with a small gray cylinder, and the death messages weren't nearly as off-the-wall (pun intended!) as Omega's ("killed by a move worthy of Clouseau").