If I had serious money to invest into the history of the hobby, I would buy as many copies of the Beholder 'zine as I could. There has always been something about the British take on D&D that appeals to me.
The first alternate magic system in this ongoing series will be a spell points system that first appeared in Beholder Issue 3. This was published in 1979, hence the title. Thanks to screen captures on the Mesmerized by sirens site, I was able to read about this fun system. For the purposes of giving credit where credit is due, I'm going to assume that Mike Stoner was the author of the system. To cover all bases, credit should go to all four authors of issue #3, Guy Duke, John Norris, John Stoner and Mike Stoner.
The system boils down to spellcasters gain a certain amount of spell points per level. Every spell that appears in the 1st Edition AD&D Player's Handbook was provided a point cost to cast. The rules for memorizing or praying for spells were altered a little. Instead of a large block of time required to gain spells, the level of a spell determined how long it took for a spellcaster to commit it to memory. As you would imagine, higher level spells required more memorization/prayer time.
The original article featured four types of spellcasters, Clerics, Druids, Illusionists and Magic-Users. For the sake of this post, I'm only going to look at Clerics and Magic-Users.
Important note about Clerics, in this system, they can spells at 1st level. Depending on the spell they prayed for and the Wisdom score of the character, they could potentially cast as many as six spells. For example, a Cleric with 18 Wisdom would have 6 spell points available to use per day. Detect Evil, Light and Remove Fear spells each cost one point. So in an extreme case, the Cleric could keep casting Light and Detect Evil all day.
How it tends to work out, though, is that a 1st level Cleric starts with 4 or 5 points a day. Since a Cleric has only has a 4 or 5 point capacity, it is likely that at least one spell will be Cure Light Wounds, which costs 2 points. Another useful spell is Bless or Sanctuary, each of which costs 3 points. The 1st level Cleric is still a lot more powerful than a standard Cleric of the same level. However, this changes as both types of Clerics gain levels. A 5th Level Cleric under this system is about equal to a standard 5th level Cleric. By sixth level, the standard Cleric is a much more potent spellcaster.
The reason for this shift is that in this spell point system, a Cleric gains only about a few points per level. Higher level spells can cost 15 - 20 points per spell. Whereas a standard 6th level Cleric gains the ability to cast 1 4th level spell, 1 3rd level spell and two spells each of 1st and 2nd level, the 6th level Cleric in the spell point system has barely enough to cast a 4th level spell and other spells. If the 6th level Cleric in the spell point system memorizes the Exorcise spell, that would likely be the only spell he or she cast that day. With some creative wrangling, a 6th level spell point Cleric, as written in the article, could pull off the same number of spells the traditional Cleric has. By 8th level, though, it is mathematically impossible. The traditional spellcaster will have more and better spells available to cast, no matter what.
Instead of seeing this as some kind of flaw, however, let's look at this as a feature. One thing that this magic system implies is the Law of Diminishing Returns. Sure, an 11th level Cleric can cast a 6th level spell, but if that same Cleric casts a Heal spell, he or she will only be able to cast a Cure Serious Wounds before running dangerously low on spell points. This makes Clerics less of a medic at higher levels because they will be limited to only a few healing type spells per day. The system, as written in the article, makes healing spells much more expensive than utility spells. This makes a Cleric much more likely to use the cheaper Divination type spells. This makes them more "cleric-y" to me as they focus more on contacting their respective gods instead of replenishing everyone's hit point batteries.
Looking at Magic-Users, something similar happens. It takes 6 levels for the spell point Magic-User and the traditional Magic-User to be equal, but at 8th level, the traditional Magic-User will always be able to cast more spells and more powerful spells than the spell point Magic-User. Again, this system promotes the Law of Diminishing Returns, you will have to be a very powerful Magic-User to be able to hurl multiple Fireballs around. In this system, a 12th level Magic-User could hurl three fireballs in a day, but only if the spell caster has an INT of 16 or more. Unless the Magic-User had an INT score of 17 or 18, those three fireballs would be the only spells cast that day. Talk about the five minute work day...
So this system works in two different ways. For one, it works great as a Hedge Wizard/Shaman type of system. The number of spell points available is determined by WIS or INT scores. Even a creature with animal level intelligence could possibly gain 1 spell point to use per day. Imagine a wizard's familiar with the ability to cast Mending once per day. Maybe a canine familiar could cast Burning Paws once a day. My favorite, however, would be an animal companion that could cast Message once a day. A character with those kinds of familiars are quite interesting.
Beyond familiars, though, a GM can create all sorts of spell casting creatures. Hobgoblins could have a handful of points (maybe up to 12) to spare. They certainly won't be throwing any Fireballs, but a Hobgoblin Hedge Wizard could sling a Magic Missile or two, creatively use Message, Magic Mouth or Mirror Image. It could also Enlarge an ally and create even more havoc.
Since the system focuses on spellcasters employing many lower level spells and very few higher level spells, it also works well in more Swords and Sorcery type campaigns. I could see a lone adventurer coming to rely more on his or her ability to trick rather than magical firepower. At first, sure, using a bunch of Magic Missiles and Burning Hands to walk through a couple goblins may seem easy, but they can cast similar spells.
I'm over 1100 words at this point, so I'll stop. Hope this provides you with some ideas to use this system in your own game. Feel free to use the linked document that adapts this system for use in the retroclone of your choice.