In 2018-20, I conceptualized a tool called Retrospective, which is an automated diary based on data (“records”).

The idea was to pick any day in the past, drag a time marker, and loop through (personal) timestamped data. In the concept, you can see:

• a sleep cycle report from a health tracker, integrated with calendar data
• a report from a hypothetical task manager and film streaming service
• a Google Location history report
• a Spotify playback history report

As for the “why?” of this tool, the main reason was that it would be interesting to see “quantitative” context for any “qualitative” diary entries around a day. This is basically what Apple’s Journal app has since done, in part, with automated prompts.

It might also be useful for research purposes, to figure out what you did on a certain day (for whatever reason you may have!). I’ve since implemented a tool to do this with browser history.

More broadly, with more data and more complicated app logic, it could help you extract useful insights from personal data. The independent app Exist is doing this (I’m happy to see it still is, in 2024, at the time of writing), and big tech health apps are generally doing this with your health data.

Finally, one more angle for an app that requires personal data to be accessible, is to preserve personal data. Cloud services that contain much of our data today are likely to, at some point, be shut down or transformed with loss. This old X thread provides some more context.