I was wondering if anyone has come across a system that allows players to create their own spells / abilities?  I'm working on a game system that incorporates this and was hoping someone could give me some reference material to study.

Thanks!

Well the best example of a system which allows players to define their capabilities, whatever they maybe is the Heroes System By Steve Peterson.

In the system everything that you can think of is templated as an effect. If one wants to build a gun, then one does so by starting with the end result. A Ranged Killing Attack (deals lasting and even fatal damage), then one applies limiters to it like It's a focus, which means the RKA can't be used without the character possessing the focus. The character might be a gadgeteer or otherwise possess the ability to make/aqcuire more than one of these pistols. If the character however can not simply replace the focus, and can actually lose the gun more or less permenantly, then one would go a step farther and apply the Independent limiter to it.

Another game which has a somewhat more nebulous implementation of the effects based character create abilities system is Mage: The Awakening by White Wolf.

I hope that helps some.

That definitely gives me a point to start from.  ^_^

Thank You!

Sorry for double post (I didn't find an edit button).
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I guess what I'm really looking for is a system that gives a large list or table of attributes you could potentially give to a spell / ability / weapon etc. and then restrictions that would be applied to it if you chose to use that attribute.

For example: Attribute: single element (fire, ice ect.) - no restriction
                    Attribute: dual element - +1 to spell lv
                    Attribute: Area of Effect - +20 mana cost
                    Attribute: does 3d6 dmg - +15 mana cost (if spell) +500 currency (if weapon)

Something to that effect.  Of course the asthetics of the ability would have no impact.

Yeah, that's Hero System you just described. Others have done it, but original's always the original.

OK,  thanks for the input.  I'll go find an SRD for the hero system or go by the book.

i've kind of worked on systemizing 'supernatural abilities' that kind of sounds like what you are talking about.

i've toyed with the idea in a diceless model where you spend points to augment abilitites, as well as a randomnized resoulution mechanic model.

these are the basic concepts.

1. like you said, you get a basic element.  i was working within a martial arts structure, so i had the five chinese elements.  fire, wood, earth, metal, water.  in theory, it can be done with any kind of basic 'element' or 'power.'

these elements are given values which represent the character's mastery over them.  using it conjures the element in your hand...

2. then, their are ways to change the spells called augmentations.
The Basic Augmentations are as follows.
Time - allows spell to last longer
Range - allow spell to be cast far away
Size - increases the radius of the effect of the spell 
Control - can single out # of targets within area the spell reaches

Augmentations are rated on the same scale as the spell, and the number would denote your ability to manipulate the element in any given way.

3. Then there are advanced augmentations I called manipulations that allow further complexity to be added to the spell.
Combine - can combine spells from different elements
Brew - can imbue potion with spell
Trigger - can cast spell to trigger at certain event
Enchant - can imbue one-use item with spell (ie. Flaming arrows)

Then there should be some really high level ways to manipulate the spell.
Artifice - can imbue permanent item with spell
Transform - can change object/person into element/spell

This list is not quite exhaustive, but it pretty much covers the basics of 'spellcasting.'

with Fire, Range and Size, you get the traditional 'Fireball' spell.  Throw 'time' into it, and you get 'Wall of Fire.'  it eliminates the need for traditional 'spell lists' and allows player creativity to run the game.

some examples
You can Combine Fire and Metal, Augment with Time to conjure yourself a Fire Sword.
With Water and Time you can float, (levitate).  Add range and you can Fly.

there has to be a maleability to the system, and a point-buy or skill test to use it and keep it balanced.  i like the idea of taxing mages for using too many augmentations/manipulations.  i like idea of limiting these based on some kind of geomancy skill or something, and also giving them a learning curve, but that's really system/setting dependant.  the idea is that with a list of 5 elements, 4 or 5 augmentations and 10 manipulations or so, you have a pretty inexhaustible magic system that rewards players for being creative.

So, say you want to craft metal armor for you and your 4 adventuring companions before you enter battle.  Your stats are as follows.

Metal - 4
Water - 2
Range - 3
Size - 3
Time - 2
Control - 4
Combine - 2

You have 10 Magic points to spend per round.

You spend
1 Magic point to activate your Metal,
1 point to activate your water to allow them mobility
and 1 point to combine the two elements. 
Then you want to increase the size to get enough metal to cover them all, so that's another 1 point. 
You need to reach your freinds with range, who are far away.  here, the GM says, 'since your range is only 3, you'll need 2 points, because they are 6 range increments away...'
you need to activate your control, so it hits only your freinds.  that's 1 point. luckily, you only have 4 friends, if you had 5, you'd need to throw in another point.
and finnally, you need to increase the time, so the armor lasts more than one 'round'. 1 point for 2 rounds... damn, let's give them 4 rounds, i don't want to have to cast this spell again. 2 more point. that's 9 points, but now my friends are covered in a liquid sheen of metal that has a protection of 4 (my power over metal).  sure, their speed is limited to a 2 (my power over water) but no one will be able to hurt them.
and i have 1 point of manna left to spend this round (to protect my ass from that incoming arrow with a quick burst of a metal shield)

my impulse was to keep numbers low.  maybe 1-5 for each power/skill level.  maybe a manna-pool type mechanic for the diceless game, and a tax-resistance type mechanic for the dice resolution version.

these are just the basic concepts tailored to a wu xia martial arts style system.  if they are useful and you're interested, i'd be willing to discuss the theory of it further.  i've never really got to see them in play.

-jonathan
 

Also look into the game Godlike, it's ala carte method for doing superpowers might be of interest to you.