KeepMood is an open source mood tracking app. If you know Daylio, you might recognise this.
KeepMood actually shows you a daily graph!
I am currently in the process of implementing more graphs.
All data is stored on you own device in an SQLite database in this app's data folder. No data is ever shared with anyone.
KeepMood is not available in the Play Store, because I don't feel like paying. I am planning to release on F-Droid and building release versions here on GitHub.