If you are referring to the Five Mother Sauces, then, brown
stock can be made into Espagnole sauce, by adding roasted mirepoix
(onions, carrots, and celery), as well as a rich brown stock, and a
dark roux... Tomato can also be added, if desired. Once you have
made the Mother Sauce, there are many derivatives that can be made,
such as: Demi-Glace (a reduction of Espagnole, that is much more
flavorful), you can add Mushrooms, and Sauce Diable (which is the
Demi-Glace, with chiles, tarragon vinegar, and shallots added)...
You can pretty much add any of your favorite ingredients to the
Espagnole, to create your own sauces.