Android App recorder for certain tasks

Question

Basically, I am looking for an Android app that every day (or possibly in other intervals) offers me the option to "check", that I did something, like for instance taking medication. This is because I sometimes forget, whether I actually did something important or not, especially if it is easy to do. At a later time, I should then be able to look at something like a calendar, which shows the days I did said task.

It would be great if the app could handle multiple tasks simultaneously. Another useful but not necessary feature would be specifying how much I did something (like how often or for how long) and displaying statistics for this task.

Answer 1

^{Amazingly, just 1h after having seen your question I've noticed this app at F-Droid. Didn't try it myself, but looks like what you want:}

Loop - Habit Tracker seems to fit your needs:

Loop helps you create and maintain good habits, allowing you to achieve your long-term goals. Detailed graphs and statistics show you how your habits improved over time. It is completely ad-free and open source.

^{Loop (source: Google Play; click images for larger variants)}

So how does it meet your requirements?

• offers me the option to "check", that I did something: Yes. And it's you to define the "somethings".
• something like a calendar, which shows the days I did said task: Check, it's there.
• handle multiple tasks simultaneously: pretty much looks like, yes.
• displaying statistics for this task: that too, yes.

As initially mentioned, Loop is also available at F-Droid. It's free and open source.