In late 2010 I wrote a tool for myself, meometer.
A pomodoro tool where you set your intent before acting, the first version—which I still use—runs on desktops via Adobe AIR and uses SQLite making it a tidy full-stack thing if you count full-stack as pixel-to-db.
I migrated from Windows 7 to Linux for pleasant, awakening few years, and now on Mac for a year.
Meometer followed me the whole time.
Which means I collected 6.5 years of data on myself.
I'm about to dissect myself with Python and some good old fashioned machine learning.