Dragonfire adepts were a Third Edition class introduced in Dragon Magic and free as part of that book's excerpts (though they are missing their invocations and can't be played with just this info). They are like warlocks in that they get invocations and a new form of attack, which is a breath weapon. Unlike warlocks, they don't have to blow any invocation slots to change their main form of attack, because they get breath effects which are basically like blast and shape invocations except they can't be traded away as you level. While DFAs share a few invocations with the warlock (Walk Unseen, Voidsense and a few others) and a feat exists to take invocations from the other class but 2 levels higher (rarely worth it), their list is otherwise unique to them and they have some goodies that warlocks just wish they could have.
The main toy they get, which pretty much defines the optimized Dragonfire Adept, is Entangling Exhalation from Races of the Dragon. You can get it at level 1, and it lets you cover your foes in sticky flaming bukkake.