Let’s consider the warlock and the eldritch blast ability. The warlock as a D&D class was first introduced in the 3.5 supplement Complete Arcane, and then perpetuated as a core class in the Fourth Edition Player’s Handbook. This is notable because it is one of the first appearances of a class with at-will spell-like powers. Other than the blast ability, the warlock is basically a slightly tougher magic-user with a more custom spell list (though the spells are called invocations).
In the original game, all weapons did 1d6 damage. Thus, a magic-user with a bandolier of daggers is not all that different mechanically from an eldritch blasting warlock. The major difference is that the warlock cannot be disarmed short of being restrained and has theoretically infinite ammunition, whereas the dagger throwing magic user has only practically infinite ammunition (most thrown daggers can be easily recovered after battle) and can be more obviously disarmed. A warlock’s eldritch blast might also be able to damage monsters which can only be harmed by magic.
Despite the fact that daggers do not generally run out, there is a sense of scarcity associated with anything that is numerically tracked on a character sheet, and this resource management is important to the feel of traditional D&D. The eldritch blast does not break the game mechanically, but it does break the game thematically.
What if we wanted to provide an alternative to the dagger mage with slightly more arcane flavor but that avoids the thematic problems described above. Enter the cantrip scroll. Any magic-user can create a cantrip scroll. It takes one day of work and 1 GP worth of supplies. Cantrip scrolls function just like other scrolls (they take a full round to intone, do not allow movement, and are consumed when used). The alternative to the eldritch blast is the malign ray: enemy must save versus magic or take one die of damage, range as thrown dagger.
There could also be cantrip scrolls with other functions. I prefer to think of arcane magic as inherently chaotic (following the lead of LotFP), so I don’t think they should have more constructive abilities; they should be limited to minor effects consistent with an agent of chaos.
This post began in my head as an old school take on the eldritch blast. To be honest, there wasn’t really a problem to be solved (I actually quite enjoy playing the traditional magic-user with no at-will powers and only one slot for a prepared spell at first level). I was just sitting in the dentist’s chair with nothing else to do and got to thinking: how is this at-will power really any different than a magic-user with a bag of daggers?