A while back I was using two apps to keep track of things that matter to me: one counting days since an anniversary, the other counting days of a streak. Both worked fine. Both were also full of ads or sitting behind a paywall for basic features. So I decided to build my own version and do it properly: no ads, no account, no subscription, and open source from day one.
That app is Markd. It counts the days since or until any date you give it, down to the second. You can set milestones (100 days, 1000 days, whatever matters to you) and it sends you a single notification when you hit one, no streak pressure, no guilt notifications if you miss a day.
It just went live on the Microsoft Store, and it has been on Android for a while already. Built with .NET MAUI, so both platforms share the same codebase.
A few things I am proud of under the hood:
Everything lives in one local SQLite file on your device. No account, no analytics, no network calls at all.
Export and import for backups, optionally encrypted with AES-256-GCM and a password, so you can move your data between devices yourself without trusting a server with it.
Supports English, Czech, German, and French, switchable without restarting the app.
I have been answering questions about the architecture on X since the GitHub repo went public, mostly about why I kept everything local instead of adding cloud sync. Short version: sync is not the hard part, moving data to a server is easy. The hard part is handling two devices that both changed something since the last sync without silently losing one side's changes. That is still an open problem for Markd and I would rather admit that than pretend it is solved.
If you want to try it:
Microsoft Store: https://apps.microsoft.com/store/detail/9N05867SQCN8
GitHub (source code, issues, the Android build): https://github.com/jame581/Markd