If you're looking for a simple clock that can track the number of days you've been sober/clean/etc, then Nomo is perfect for you. You can create as many clocks as you need for any hurts, habits, or hang ups. Your clocks are completely private by default and will count those days for you.
If you're looking for something more, just check under the hood. Nomo has tons of optional features like an encouragement wall from the community, accountability partner searching, clock sharing, private messaging with partners, milestone awards, journaling, little games/exercises to help you refocus when you're tempted, and tons more!