Your own lastfm! Sweet if you just wanna track and get an overview of your listening habits without all the tra-ra of social connections.

How to track your own position with GPS and use the data in interesting ways -

I am especially fond of the 'magic clock' pointing to your current location (Home, Travelling, Shopping, Pub, ...) which strongly reminds me of Harry Potter wizardry. Put it in a nice enclosure and it's a really neat thing for home.

Open-source smartwatch that is fully arduino programmable (run by an ESP32), usually lasts 5-7 days and costs around $50.

Quite a few watchface examples exist online. From what I understand, the watchface is the firmware for this clock,
so no too easy changes there.

There are assembly kits with a case that can be bought for some $ more that will keep the watch a bit more safe (though not e.g. swimmingpool ready). The watch/display so far only exists in square shape.

List of quantified self resources - some outdated and some missing (Grafana would fit into many qs deployments, datasette, etc) but not bad for an overview.

karlicoss of the data liberation project HPI explains how to best store and access data moved from various points in the cloud/web/internet to your drives and why databases might not always be the best choice.

TLDR.
Save your grabbed data without any manipulation.
Let the manipulation happen every time you access/interpret the data.
If you have slices of data (mostly time frames), don't try to merge them on disk but save as extra files and merge on access/interpretation as well.
You can make use of databases for access caching since the last points generate some overhead for each access.

A free and cloudless replacement for your gadget vendors' closed source Android applications. See the list for supported devices. https://gadgetbridge.org

A versatile and extensible platform for home and life automation with hundreds of supported integrations - GitHub - BlackLight/platypush: A versatile and extensible platform for home and life automation with hundreds of supported integrations

Seems really interesting, like a lighter-weight, more programmatic alternative to e.g. HASSio.
Has a lot of plugins and connections and the blog is very inspiring.

A quantified self program for the PC - run as a commandline program and also contains an analysis cmdline tool to then query the (sqlite) database later (examples in readme).

Similar to activitywatch, rescuetime.

Very in-depth deliberations on continually exporting data from various siloed services in pursuit of more holistic quantified self approach.

A whole library of interfaces to extract quantified self data through (more or less) simple python scripts.

powers ad is explained by many of the thoughts in beepboop

Somewhat similar to activitywatch, etc.

Takes snapshots of currently open/active windows and their titles. (By default every 60s, can be more fine-grained.)
Snapshots can then be reviewed and tagged automatically through writing a categorization config file,
e.g. tagging all browser titles with ^.*//scholar.google.com/.*$ as Research, or as Research:Papers, to get even more finegrained.

Allows idle-detection and tagging to remove.

Data can be exported out to .log files or to csv files.

To-do list & time tracker for programmers and other digital workers with Jira, Github, and Gitlab integration - johannesjo

An android app for tracking personal data and creating custom graphs - SamAmco

Self-hosted habit tracker and event logging web app. - AppMini

A goal, task & habit tracker + personal dashboard to focus on what matters - onejgordon

Loop Habit Tracker, a mobile app for creating and maintaining long-term positive habits - iSoron

Quantified Self Personal Data Aggregator and Data Analysis - markwk

Many ipynb data analysis examples for toggl, todoist, lastfm, goodreads, and so on and so forth

Shows how to download, aggregate, import, organize data, correlate, unify and more

Time-tracker with server/agent components. Open source and coming along somewhat nicely.
Plugins for e.g. editor (vim) and terminal already exist but I have not tried them extensively.

Could integrate nicely into personal data scraping pipeline.