Ever since I played Final Fantasy 3 (6, whatever) as a kid I've been enamored with the idea that you could totally mix Magic with Technology. Before then I had always thought the two were mutually exclusive, as if inventing fire arms would inadvertently cause all the pixies in the world to spontaneously combust or something.
Its obvious I don't feel that way any more - While I occasionally like to play the two as polar opposites, most of the time my skeptical brain asserts that they probably aren't all that far apart and it would be cool to have Promethean-esque adventures who bridged the gap between the two effortlessly. So yeah, here you go!
I should say there is nothing keeping you from making this class entirely technological OR magical. Just change the name to just Engineer, Artificer or something to that effect and your gold.
Attack: As a Thief
Saves: As a Thief
Hit Dice: As a Thief
Weapons: Dagger, Club, Mace, Crossbows and Fire-Arms or any suitably advanced weaponry
Armor: Up to an include Leather
Level Advancement: As a thief
Tinker: Every Magitek Engineer is naturally adept with mechanical devices. Not only can they automatically discern a device's function after a night of study, they may also attempt to repair a broken item or nullify other mechanical hazards, such as a broken power reactor, loose energy cords and the like. The length of time or materials required for such attempts are left to the DM's discretion, but both require an intelligence check to accomplish. Failure by more then 5 (Or a natural 20) means that the device is broken in a spectacular way or that the hazard becomes dangerous for the engineer.
Gadgetry: It can be assumed that the Engineer is constantly inventing, creating and cannibalizing any number of minor devices. These are generally small and reasonably portable, though larger devices are not impossible (if a bit rare).
Anytime a Magitek Engineer is called upon to make a stat check of any kind, they may declare they are utilizing a gadget to solve the problem at hand. Doing so means they may use their intelligence score instead of whatever stat the check was originally meant for. During the process the player may name the tool being used or even describe its mechanism a bit; at the very least they should explain how the gadget is going to accomplish the task presented.
If the skill check succeeds, then the item is a success and the task is successful. Failure indicates that the item is a dangerous failure and the Magitek Engineer is faced with repercussions as dictated by the DM. If the check is failed by five or more (Or a natural 20 is rolled) the item literally does the exact opposite of what the Engineer intended.
If they so desire, an engineer may mark down a Gadget used in a success as a their favored item. Any future attempts with this particular gadget will allow for one re-roll; however it may only be used for the specific task the Item was originally designed for and the Engineer may only have one favored item at a time. The item can be disassembled overnight, allowing for a new gadget to be named as the favorite after its initial testing.
Perfected Prototype: All the testing, research and failures that the Engineer endures each and every day does pay off; every once and a while they manage to get a gadget to do exactly what they would like to do in a consistent manner. At 3rd level, the Magitek Engineer creates a device that replicates a single first level wizard or cleric spell three times a day. Afterwards, at 6th and every third level after that the Engineer can make a new item that functions in the same manner, save for that a spell of one level higher can be selected for the device. (I.E; A 2nd level spell at 6th, 3rd level at 9th, and so on, maxing out at a 4th level spell on a prototype at the 12th level of experience) Each spell functions at a caster level equal to the level that the Magitek Engineer had attained at the item's creation.
Please note that the spell chosen is purely for mechanical effect - the actual flavor and physical nature of the device is entirely up to the player (Within reason, of course). Also note that while the device emulates a magical spell, it is not a traditional magical effect but a magiteknical one. The exact nature of magitek is dependent upon the campaign setting and the DM running the game.