First, design goals. One of the things that I found dissatisfying about Traveller psionics is that it is a very, very limited-use resource. Playing a character whose primary function is psionics is nigh-impossible, because psionic strength points are very limited, and your ability to use more psi talents decreases as your Psi DM drops. This was something I wanted to avoid in the design for FantTrav's magic system. However, I did like the relative simplicity of Traveller's psionics system - it's about 10 pages, all told, including spell listings. In comparison with D&D's magic system, it is positively minimalist. Finally, in core, there are five skills associated with it (telepathy, telekinesis, awareness, teleportation, and clairvoyance). I feel that this is about the right number; it's hard for any one character to be good at all of them, which means that at least two characters can 'do' psi in the same group without stepping on each other too much. On the other hand, it's also not so many skills as to be mind-boggling.
Initially, I tried to look at all available effects producible by magic in D&D, and then to group them into categories. This proved to be a massive and fruitless task. Instead, I ended up with something... a bit simpler. Five categories, five skills, grouped heuristically and intuitively, and with effects loosely defined. Today, I present the arcane skills, with divine coming soon.
Also, note that with each skill is a list of sample effects. These are just that: samples, not binding restrictions on the use of the skill. Season to taste.
Wizardry: Wizardry is the study of the subtler manipulations of arcane magical forces. Skilled wizards are adept at creating illusions, manipulating the minds of others, seeing across great distances, the construction of complex wards, teleportation, and the destruction of other magical effects. Wizardry is primarily powered by Education, as it depends on careful study of arcane mysteries, though Intuition may sometimes be suitable for trying untested, experimental magics in the heat of the moment ("I need to create an illusory smell, but I only know how to create illusory images... tricky."). After you do it a few times, write it up, and publish, though, a particular effect may switch to Edu.
As a general guideline, if a Wizardry check fails with effect -1, the spell fizzles but the caster knows what they did wrong, and if they begin re-casting the same effect immediately following the failure, they gain a +1 DM. Between effects -2 and -5, the spell has failed, and at effect -6 or lower, the spell has opposite the intended effect - you make the party fighter more vulnerable to fire, bolster an enemy caster's spellcasting check, or otherwise make life more difficult. Teleportation is an exception to this guideline; at effects below -1, you just end up somewhere you weren't planning on going, with effect below -5 resulting in going places you really, really didn't want to go to (the court of the enemy king, or Hell, for examples).
Create an auditory illusion to muffle your footsteps - Routine (+2) Wizardry + Edu, 10-60 seconds, as part of a skill chain with Stealth (incidentally, I aim to make the skill chaining rules more merciful, and to make extensive use of chains - but that's another post).
Convince a guard that these aren't the halflings he's looking for - Average (+0) Wizardry + Edu, 10-60 seconds, with a negative DM equal to the guard's Int DM, as part of a task chain with Deception.
Counterspell an opposing spellcaster in combat - Difficult (-2) Wizardry + Int, 1-6 seconds (significant action). You apply twice your effect as a negative modifier to the opposing caster's skill check to cast.
Disable / dispel a static ward outside of combat - Average (+0) Wizardry + Edu, 1-6 minutes. Some modifiers may apply depending on the type and magnitude of the ward.
Teleport a short distance during combat - Average (+0) Wizardry + Edu, 1-6 seconds (significant action). You may teleport yourself and your equipment up to 6 meters, plus 1.5 meters per point of effect. Teleporting an ally this way is Difficult (-2).
Teleport across the continent, taking all of your allies and their gear with you - Very Difficult (-4) Wizardry + Edu, 10-60 minutes. Additional penalties may apply if you're trying to teleport to somewhere you've never seen, or bonuses if you're going to a place you have ritually prepared or are overly familiar with (your sanctum, for example).
Sorcery: While Wizardry is the subtle, calculated manipulation of arcane forces, Sorcery is the incautious channeling of raw arcane power. Sorcerers are good at flinging fireballs, calling down lightning strikes, telekinesis, flight, calling elemental beings from the very fabric of nature to their service, and similar effects. If it's big and flashy, it's probably sorcery. Sorcery runs primarily on Intuition; most sorcerers don't have a damn clue what they're doing, and don't care as long as it works. Sorcerous rituals for doing things like calling fire and brimstone down to level a city, however, may run on Education, as careful study is required to enact effects of that magnitude.
As a general rule, if a Sorcery check fails with effect -1, the caster should be given a choice between having the spell fail / fizzle, or having it succeed with collateral damage to the caster, a party member, or something else valuable. If a Sorcery check fails with effect between -2 and -5, it just fizzles, and with -6 or below, it backfires completely.
Attack a nearby foe with elemental energies - Routine (+2) Sorcery + Int, 1-6 seconds (significant action), inflicting 2d6 damage plus your effect. You may increase the difficulty of the check to gain +1d6 damage per -2 DM taken, but this must be declared before the check is made.
Attack a group of nearby foes with elemental energies - Average (+0) Sorcery + Int, 1-6 seconds (significant action), inflicting 2d6 damage plus your effect to each target. For each target beyond the second, you take an additional -1 to your check. As with Attack a nearby foe, you may voluntarily increase the difficulty to gain extra damage; see above.
Armor yourself or another in telekinetic force - Average (+0) Sorcery + Int, 10-60 seconds. The recipient gains Armor equal to your effect for ten minutes, which does not stack with nonmagical armor. You may voluntarily increase the difficulty of the check to increase the duration, at a rate of +5 minutes per -1 DM taken in casting, but this must be declared before the check is made.
Armor yourself or another in flame - Difficult (-2) Sorcery + Int, 10-60 seconds. Each opponent who strikes the recipient in melee for the next 10 minutes takes 2d6 plus your effect points of fire damage. As with Attack a Nearby Foe and Force Armor, you can increase the difficulty of the check to increase the damage or duration; see above.
A few design notes:
Wizardry is more of a support school - it's good for making everyone else better at what they do, whatever it may be. Sorcery, by comparison, is great at combat... and not a whole lot else. Sorcery's "increased risk for increased reward" theme also seemed appropriate to the reckless, intuitive nature of the school. The omission of flight from the sample sorcery effects is intentional; flight is a sufficiently powerful ability that it should not be given lightly, and its utility varies significantly across circumstances. Overland flight for the party might be of a 'capstone' difficulty on part with cross-country party teleport, but combat flight is significantly more powerful than combat teleportation. Assign difficulties wisely.
Next time: divine magic.