Author here! I had searched around but didn't find any existing app that matched my requirements. A few that immediately come to mind:
1. I have sole ownership of the data
2. The data is stored in an easily parsable format (TSV)
3. Duplicating a recent activity takes one tap
4. Pie and area charts are displayed in the app
My app is open source and available on GitHub[1] for any Android developer to compile for themselves, but if there's enough interest I can also get around to packaging it up for the Play Store/F-Droid/etc.
I've recently began to take life tracking semi-seriously and mostly use "off the shelf" tools. A good all-around dashboard is https://exist.io/, capable of pulling data from multiple sources like RescueTime and various health-monitoring applications that come with smart watches.
Did you consider any existing apps before making your own? Are there any apps like this that are available for download?