Maggi, not "Maggie." It's a condiment / flavor enhancer / seasoning sauce, now made by Nestle. It's something like soy sauce but with a great deal more going on. It's hugely popular in all sorts of regional cuisines. and not just with or instead of soy sauce. You'd be surprised where it turns up - Polish and Mexican cooking, for instance.
When I tell the story of how I learned to make congee, and the final step in the process of going from "something missing" to "just right" was a few drops of Maggi, the Asians always laugh because it's so true.
Salty, sweet, complex, tons of umami. Great stuff. Get some. Try it.