I usually keep my rpg stuff away from here....

But I'm sleepy and I have a TRULY SCIENTIFIC fluff/crunch magic system I thought of,
and I don't want to forget it.

Basically it began with thinking, 'how would an abductee from our world to a fantasy one be
able to use local magic?'

Midichlorians were thought of at one point.

Now, of course, this might also work as a magic system for a story of some sort. It also combines nicely with Scifi elements, as 'magic' of this type might only exist on a single planet.

PREMISE:
Okay, basically, in our scientific fantasy world, there is a thing called magic.
It's physical representation are floating glowy things, called 'motes', 'mana' or 'spirits'
Wizards draw magic to themselves, craft spells, and do things like blasting, farseeing, levitation, and so forth.

Through practice, wizards can turn a certain amount of magic into spells. they can cast these very fast, and they can be taught.

Magic can even be passed forward in family.
Basically, a very standard world with magic.

Technobabble:
What is going on is this:

The glowy things are creatures, of sort. They can do pretty advanced things with electromagnetism and Van  Der Waals forces.
They live and breed in trees, as a rule, but may inhabit a living human, too. (this can be somewhat harmful, and thus we can get 'frail' magicians )

Most 'magic' things are done by commanding these creatures. The typical list of commands taught are:
Draw, repel, emit, observe, move, mimic, grab.

Each mote can learn one thing, but multiple motes can form composite creatures.
standard, 'light' magic: motes vary from translucent to bright glowy light, emit a small amount of light and heat typically.
'dark' magic : variant creatures, who absorb light much more efficiently. absorbing  IR light absorbtion makes the areas colder, and they default from lightly dark to black, typically. even when they emit, it's typically shades of red or purple.

Motes can naturally grab each other, but they can be taught to grab other things.
Spells are formed by, say, connecting a mote taught to move to a mote taught to emit an EM radiation burst.

A typical use of magic would be to draw in magic, teach the magic one to three commands and using a combination of these commands to create effect. a combination of observer, mover and grabber, can observe hand signals from the mage, move quickly, and grab onto objects.

Flocks of these creatures would naturally form larger symbiotic entities analogous to 'faeries' and other mythic creatures.

Magic-users use props as hosts for these creatures - it's necessary to form some sort of symbiosis with Magic to be able to control it, but you don't want a bunch of EM emitting creatures livin inside you, as a rule. However, a nice chunk of wood might well contain an entire colony of domesticated motes.

A skilled mage might be able to replace a removed limb with a magic copy (probably using some sort of crafted part as a base), but chances are, it would slowly corrode and replace the host body from the contact surface upwards.

Magnets might interact in a rather interesting fashion in such a setting.

Cory Doctorow

Is a published writer. He also puts his books online, under the Creative Commons license.

The books are mostly 20 minutes into the future Scifi.

I started reading the full-length novels, from "DOWN and OUT in the Magic Kingdom" onwards, and, well, basically, the first book I liked thus far, was 'Little Brother'.

All the books present some ideas integrated throughout a story, and sometimes things work, oftentimes not.

The ideas are always quite neat, but the viewpoint characters are often a touch too unlikeable, in my opinion.
I'm currently reading 'For the Win', which has thus far jumped from a viewport to the next, which seems to have stalled my enthusiasm. 'Makers' was basically okay, but there was a longer chunk following a single viewpoint in the start, so when it changed, I was already deep into the story.