With that in mind, I've made developers using tannic acid. The first attempt, I took the stock formula Pyrocat-HD formula and simply substituted tannic acid for the pyrocatechol and processed it like Pyrocat-HD. It worked, but the negative was pretty underdeveloped.
So I made another developer, this time following the Pyrocat-HD formula, but using 10 times more tannic acid than the previous developer. That worked and gave negatives that had an acceptable contrast index and it had a stain similar in color to Pyrocat-HD as well.