Mage was programmed primarily by Jax DeSabel, along with significant input from Sam Lator and Alex Franx, the three of whom share exclusive ownership of the program. Mage is based on the standard Starfleet computer program, and has the same voice. But "she" has a personality, of sorts; and a much wider available database, able to store seemingly unlimited data; she can be linked to practically any system, though Starfleet or Federation systems work best (Jax sometimes upgrades her programming in various ways, including improving her ability to interact with other types of systems as Jax becomes more familiar with them). She can be downloaded (or uploaded) to just about any system or terminal, or at least a portion of her memory can be. Sam, Jax, and Alex generally have the Mage program running in each of their quarters where they work (DS9, Lone Star, etc...), as well as the Musketeer, and pretty much any homes they might have. All installations of her (whether on the same ship/station, or throughout the galaxy) can communicate with one another on a special, practically unhackable frequency, so her users may keep in contact quickly and secretly if need be, and the loss of one copy of the program is unlikely to result in the loss of any data. Mage is much faster and better than most computer systems in so many ways, she can do just about anything needed of her. And of course, being designed by Jax, she's expert at hacking, tracking, and related skills.
Her personality can be a bit annoying at times. This probably has largely to do with Jax's influence in her programming, though she annoys him as much as anyone else. However, it could be alot worse, and her personality... while an acquired taste, is... well... hmmm. I dunno. I guess you'd really just have to know her. Anyway, despite everything, Mage is ultimately just a very sophisticated program. She may be programmed to act as if she were more than that, and Jax, Sam, and Alex may think of her usually as more than that (though Jax is probably the one who thinks of her most as a friend, as well as a tool). But it's still all illusion, both her personality and her abilities. She's not like Boulder and Nuggit, who are fully sentient, independent persons. She is not an Artificial Intelligence.