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Acid Splash

We start out with a spell that's so simple it's boring, one of the most basic offensive cantrips in the Player's Handbook. In practical terms, what this spell allows you to do is toss a thin mist of toxic vapor at a target (or two) within 60 feet; if they don't make a Dexterity save, they get a face full of sulfuric acid. 

Now, in D&D terms, this isn't really that big a deal. It does a maximum of 1d6 damage, and has a 60' range (which is basically D&D standard range for an offensive spell). It's minor enough that it's usually an afterthought, the damage-inflicting cantrip you pick if you forgot to get Magic Missile. But put it in the real world!

For one thing, 1d6 isn't much in a D&D campaign, but it's within the average hit points of almost any normal human, or, as alt-right weirdos and the game calls them, "NPCs". 6 points of damage is more than enough to kill a normal human! And even a 1st-level wizard with it can do it twice a round--basically once every three seconds--as often as he wants!  That's pretty powerful, and there's nothing in technology that could easily replicate it short of carrying around some kind of terrifying tanker rig full of acid and a projectile sprayer, like some deranged pest control specialist.  And at high levels, damage goes up to 4d6!

In game terms, this is the equivalent of a small back-up pistol, something you carry in case your main weapon jams. But it the real world, it would turn you into a creature of nightmare, wreaking terror as you turn everyone in sight into a screaming, disfigured Toxic Avenger.  Gross!

Real-World Rating (1-10 scale):  8 [Very Effective]

Aid

This one, like a lot of buffs, is hard to figure out. In practical purposes, it lets you raise your ally's hit points by a certain amount for 8 hours. This isn't bad -- it just has limited applications. 

Of course, it's very valuable if you're about to get in a fight. You could probably make good money casting this on professional boxers or MMA fighters before a bout. But it doesn't have any other real practical applications, and in the long run, it's less effective than steroids.

Real-World Rating:  5 (Effective But Limited)

Alarm

The idea of having an alarm set specifically to you, that only you can sense, and that can be set exactly by you alone to a given area, is kind of neat, but all in all, this falls into a category we like to call JUYP, or Just Use Your Phone. This doesn't do much you couldn't accomplish with a cell phone app and/or a modestly priced security system.

Real-World Rating: 2 (Mostly Pointless)

Alter Self

This 2nd-level throwaway is actually one of the best low-level spells -- depending on your interpretation of how magic works in the 'real world'. The Player's Handbook is understandably mum on the question of whether or not illusion magic could fool an AI or a machine (say, a video camera); the only insight we have is that Illusion school spells aren't effective against constructs, except under particular circumstances too boring to get into.

But the thing about Alter Self is that it isn't an illusion! It's a Transformation spell, meaning that you can literally, physically turn yourself into any other person for a whole hour, and no one could detect you! There's no save! It's a perfect physical duplication of anyone else on Earth*. Nobody, nowhere, nothing would be inaccessible to you; you could go anywhere, and you might cause confusion, but you'd never raise suspicion -- until it was to late. You could impersonate a dead person. You could make yourself a complete, undetectable clone of the President of the United States. You could be anyone who ever lived, and make that person do anything. You could steal anything you want, infiltrate anywhere you chose to go, and throw any situation into total chaos.

And that's not all! Aside from this incredible power, which isn't that special in D&D but would be an ultimate-weapon level ability in the real world, you can also breathe underwater and swim at walking speed, or give yourself a pretty good natural weapon (claws, fangs, horns, etc.) for the same duration of time.  And you can switch between the three options!  And if you use the "Change Appearance" option, you can change between multiple different appearances for its duration!  This is all killer, no filler. 

Real-World Rating: 9 (An All-Time Great)

Animal Friendship

A lot of D&D spells assume that you live in the frequently hostile environments of its various fantasy settings, in which, whether you're crawling through a dungeon, bedding down in the wilderness on the way to a dungeon, or having things conjured at you by a wizard who knows where a dungeon is located, you are very likely to be attacked on a semi-regular basis by monsters and fierce animals.

In the real world, though, those conditions -- and thus the need for spells which address them -- don't really exist. Animal Friendship basically gives you the ability to Charm (defined as another creature being well-disposed to you and thinking of you as a friend) a beast (defined as a normal, non-magical animal) for 24 hours. Frankly, you can get this spell to be permanent by just training most animals for a couple of weeks, or, in the case of a dog, in five seconds by giving it a treat.

Dogs, of course, are generally well-disposed towards people anyway; others are indifferent to us, and most are understandably afraid of this. Since beasts remain of animal intelligence under the auspices of the spell, it's not like they can give you useful information, or communicate with you, or become anything like a conscious ally; basically, its only value is if you're in one of the increasingly rare situations when an animal is determined for whatever reason to attack you and you use it to prevent it from doing so. You could do the same thing with a gun, or an air horn.

Real-World Rating: 3 (Pretty Ineffectual)

Animal Messenger

One of the many D&D spells meant to address the fact that its medieval fantasy setting has no reliable mass communication, Animal Messenger lets you send a short message to an ally via the medium of a tiny animal. Not only does it have lots of complications -- you have to be within 30' of an animal, the message is limited to 25 words, you have to pick a target to whom there's nothing weird or suspicious about talking to a squirrel in front of people, and how far can a bat really get in 24 hours? -- but it's a classic JUYP situation. There's nothing this spell can do that can't be done better with a text message, which is private, can contact anyone anywhere in the world instantly, and doesn't rely on being able to get clear instructions from a crab.

Real-World Rating: 1 (Worthless)

Animal Shapes

Some of the higher-level spells (this is an 8th-level) are ones that seem really impressive, but when you think about them, they aren't actually all that useful. This is a good example: it's really cool (you turned your pal into a bear!), but what do you really do with it?

If your friend (it's only usable on willing subjects) is a high-level character already, odds are they're already more powerful than whatever you turn them into. And the peripheral benefits of turning someone into an animal -- say, turning them into a mouse so they can be small and get into otherwise inaccessible places, or into a crow so they can fly -- are already ones you could accomplish with other spells if you're already able to cast at 8th level. Definitely a spell where the cool factor of turning your cleric into an elk obscures the question of why you would want your cleric to be an elk.

Real-World Rating: 2 (Mostly Pointless)

Animate Dead

This is the first real money spell of the Necromantic school. Depending on the level you cast at (and your ease of access to fresh human corpses), it lets you create a small army of the undead -- low-level, to be sure, but devoted to you alone -- within a couple of weeks, or a personal retinue of reanimated corpseflesh in just one sitting. The value of this in the real world, while likely a pretty mixed blessing, should be obvious enough.

One odd thing about Animate Dead is that you only have control over your zombie or skeleton for 24 hours unless you cast it again. But if you don't, the undead doesn't disintegrate or cease to exist or crumble back to dead flesh and bones; it just wanders off on its own! The fact that there are always so many skeletons and zombies around to nuisance player characters is no doubt attributable to the fact that necromancers are lazy about picking up after themselves.

Real-World Rating: 7 (Effective)

*: The wording of the spell in the PH invites some interesting speculation on how the alteration works. In terms of practical application, it seems that you can make yourself a perfect duplicate of anyone you choose; but how deep does the impersonation go? The spell mentions you can "make yourself appear as a member of another race, though none of your statistics change." In game terms (and in a game where "race" actually means "species"), this implies that you could make yourself look like an elf, but you wouldn't really be an elf except to the senses, which would see you as an elf and hear you as an elf and presumably smell and taste you as an elf. So how far does the change go?

If you impersonated someone you knew, or a total stranger, you would have their appearance, their voice, and their physical characteristics, but not their memories or their personality. But what about a DNA test? Could you fool that? What about a fingerprint test?  It's entirely possible you can't actually impersonate anyone at all, deflating this from a world-class spell to a well-intended fuckup. The spell description says "You transform your appearance.  You decide what you look like." (Emphasis mine.) So, does this imply that you're able to completely impersonate someone you know fairly well, drawing directly from your memory? Or is is more like making yourself into a drawing of another person, with your success or failure hinging on how good an artist you and how carefully you've observed them? It could be that you can't imitate another person at all, because you'd never get every detail exactly right, and that Alter Self only allows you to change into a sort of generic person:  "a king", but not "King Rodolf XII". This sort of speculation, and the answers that players and DMs arrive on, can make some campaigns incredibly fun, and others unbelievably annoying.