ArrowStorm, DaggerStorm, or SilverStorm are the use of missile weapons as the primary way to deal damage in NetHack.
The preferred roles to do this are Rogues and Rangers, for their weapon proficiency and for their +1 multishot bonus, but roles with high skill in missile weapons also work (particularly Wizards, Tourists and Valkyries for Expert daggers). In addition, a Ring of increase damage would also be of considerable benefit since the damage bonus will be added to each projectile.
As a Ranger or a Rogue you get +1 multishot for thrown daggers, even when dagger is Unskilled, so, even as an early-game character, you can probably deal more damage by throwing daggers than by using a melee weapon, even in melee range.
The best type of daggers to do this is probably the silver dagger, due to his high damage bonus (+1d20) against the silver-hating monsters, but since they are hard to find, most people end up using a stack of elven daggers or just plain normal daggers.
Rogues also get a backstab bonus (+1dXL) against fleeing monsters, for each thrown dagger; in the end game, the damage of a stack of thrown, enchanted silver daggers against a fleeing silver-hating undead, assuming that every projectile hits and the character has maximum strength, as a level 30 Rogue with Expert dagger skill:
2 skill bonus +6 strength bonus +2.5 average of 1d4 against small monsters, becomes 1d3 (2) against large +7 enchantment +10.5 average of 1d20 silver damage against silver-haters +2.5 average of 1d4 blessed damage against undead +15.5 average of 1d30 backstab damage against fleeing monsters =45.5 average for a single blessed +7 silver dagger against a fleeing small silver-hating undead *2.5 1d4 daggers thrown in a single firing =113.75 *average* final damage (112.5 against large, absolute best case is 292! damage)
Compare this to the average damage for Grayswandir, the best weapon in the game, twoweaponing it with another silver saber, with maxed skills (assuming, with the same Rogue, Expert two-weapon combat and Skilled saber):
2*( Grayswandir's double damage 4.5 average of 1d8 against any +7 enchantment ) +6 strength bonus +10.5 average of 1d20 silver damage against silver-haters +2.5 average of 1d4 blessed damage against undead + 4.5 average of 1d8 against any +7 enchantment +6 strength bonus +10.5 average of 1d20 silver damage against silver-haters +2.5 average of 1d4 blessed damage against undead =72.5 average of the blessed +7 Grayswandir twoweapon with a blessed +7 silver saber against a silver-hating undead
That said, a stack of silver daggers is one of the rarest item in the Mazes of Menace (stacks of 1d6 silver daggers are 0.3% of all the randomly-generated items), so most adventurers will settle for a stack of daggers, or elven daggers when possible, but even in that case, it's usually enough to kill most monsters before they even have a chance of landing a hit on you, since daggers are a ranged attacks, with the range depending purely on your strength (with St:25 you have 10 squares of range).
Unless you're using silver daggers, if there are spare scrolls of enchant weapon laying around, it's better to Fooproof your stack of enchanted daggers, since a lot of monsters can corrode iron, limiting your damage; it's also better to #name your stack of daggers giving it a unique name, and to set an autopickup exception for your own daggers, to help picking them up. Also, watch out when firing around water, since daggers that end up in a pool or a moat are hard to recover; better have a backup melee weapon for sea monsters.
One of the advantages of throwing daggers, as opposed to using a melee weapon, is the fact that you can use a wielded artifact weapon for the bonus it provides, and not just for the damage; Magicbane's damage is low, compared to other artifacts, but the perks it gives (MR and curse absorbing) are nice; Magicbane is a great weapon, even for Rogues (chaotics) because it also gives you a way to engrave a semipermanent Elbereth - great for the backstab bonus. Another way to scare monsters, that works at range, is a tooled horn, which is another great tool for Rogues.
Another great alternative to melee weapons, especially if you are an Elven Ranger, are elven arrows, fired from an elven bow: Rangers get a +1 multishot for every projectile, and Elves have a +1 multishot (together with a +1 to-hit and +1 damage) for firing elven arrows from an elven bow, bringing the average fired projectiles to 3.
In the early game, using daggers is probably the best choice, since they don't break, but as soon as you can rotproof, enchant (+2 or more), bless and get high Luck (9 or higher) arrows pretty much never break, so you can ditch the daggers and start accumulating arrows (they are *way* lighter - 25 daggers weigh the same as 250 arrows). Note that enchanting the bow only adds to the to-hit bonus, not to the damage, so enchanting the bow is mostly useless). You can also poison arrows, by #dipping a stack of arrows into a potion of sickness, adding damage against non-poison resistant monsters, and giving a chance of instakilling them; note that using poisoned weapons as a Lawful gives you -1 alignment.
Damage calculation for blessed poisoned +7 elven arrows, fired from an elven bow as an Elven Ranger, with Expert bow skill:
2 skill bonus +1 racial bonus +4 average of 1d7 against small, becomes 1d6 (3.5) against large +7 enchantment +3.5 average of 1d6 poison damage against non-poison resistant =17.5 average for a single blessed poisoned +7 elven arrow *3 average of 1d5 fired arrows in a single firing =52.5 average final damage (51 against large)
This applies when attacking normal enemies that are not poison-resistant, not including a 10% chance of instakilling with poison - with 14 poisoned arrows you have over 50% chance of killing an enemy, regardless of damage. Undead and demons are poison-resistant, but they suffer from the blessed damage (2.5 average). Using a launcher gives you extended range of fire, so you can get even more shots at monsters while they come to you.
Firing poisonous arrows can remove the poison coating, so after a while you may want to re-dip your de-poisoned arrows in another potion of sickness to bring the stack back together.
A way to get the "best of both worlds" is using silver arrows with a bow, usually the Longbow of Diana as a Ranger. Still way lighter than daggers, there's no need to Fooproof them, they can be poisoned and they deal silver damage against silver-haters. Again, avoid using them until you have maxed your luck and blessed them, enchanted silver arrows deal a damage comparable to a rogue throwing silver daggers:
2 skill bonus +3.5 average of 1d6 against any +7 enchantment +10.5 average of 1d20 silver damage against silver-haters +2.5 average of 1d4 blessed damage against undead =25.5 average for a single blessed poisoned +7 silver arrow *2.5 average of 1d4 fired arrows in a single firing =63.75 average final damage
Again, this is for a maximum range of 11, so, especially if you're fast or very fast, you have the time of killing monsters before they get even near you. The same advices regarding missile managing apply here.