Only saw these megathreads now, thank you for the great work. If you don't mind I'm just going to past my comment of a recent post with a similar question, but add some more that I use. If you want I can delete it

I use a variety of FOSS tools for both personal and work productivity.

For personal I use:

Nextcloud (Calendar, sync files, contacts etc, forms, availability sharing)
Thunderbird (Mail & Calendar)
Vikunja for managing all my projects/tasks. Also is very useful to have shared tasks with relatives. Another useful feature is that it can share specifics projects to people that do not have an account (for vacancy planning for example)
Tasks.org to manage Vikunja tasks in Android
Logseq for managing all my thoughts, ideas, tracking content like books, movies, videos watched
Nomie (specifically this maintained instance which has some new features). I use it to track myself (mood, anxiety, adhd, symptoms, food and drug consumption, people). It has an API so I for example can automatically insert activities from Garmin API. It is very useful to correlate things in life, or to tell the doctor if a specific symptom has flared up or not and many more things
Omnivore is my read-later off choice app, replacing Wallabag. It has an EXTREMELY polished interface, can aggregate RSS feeds, supports tags, comments, many filters and more. But the amazing thing is that it has a plugin for Logseq which automatically syncs all my highlights, notes and tags to it
Ferdium to quickly access all my important services
Syncthing on my phone, laptops and Kobo to sync Logseq between devices and books/articles from my PC to Kobo
Liftosaur for exercise routines (it has script language even) and can also track body measurements.
waistline as a substitute for myfitnesspal or cronometer
Phoneprofileplus as a sort of Tasker substitute
Sayboard for speech-to-text keyboard
Cofi to aid in making the perfect cup of coffee
Anki for learning things faster. I use a plugin for Logseq to automatically send cards to Anki, and AnkiDroid to access anki on phone
ActivityWatch has my cross-device time tracker
FindMyDevice but FOSS

For work use:

Logseq is my main tool, with the capability of connecting to Zotero, reading papers and taking notes which with queries I can leverage it to see new ideas forming. It also acts as the best logbook I've ever used through its powerful templates and queries which simplifies a lot the work of comparing results since it can all be done automatically
Zotero to manage all my papers
neovim with vimtex, ltex-ls and ultisnips to write documents in LaTeX very fast. Also have some scripts to manage vector graphics very easily using https://github.com/gillescastel/inkscape-figures
Inkscape for doing all the images for my papers since I plot my graphs in SVG. This way I can edit graphs after ploting and never lose quality
Ranger file manager
Espanso