My “Knowledge Repository” is wiki.js, a wiki software where i write only markdown pages, cause the syntax is easy and if ever necessary i would be able to just move it over to another wiki that supports markdown. It is synced to gitea (git server) so i can always just do a git clone before i do critical maintenance on the server i host wiki.js. On my android phone i use GitJournal, it syncs with gitea, automatically shows a markdown preview and stores the whole wiki on the phone so i can access it even when i have no internet. And the best thing is i can even do edits on the phone and it syncs back to gitea and from there to wiki.js.
I use it for less than 2 years but a recent paper backup was over 130 pages long… I use it to document how my servers are set up, any software/linux tricks and kung-fu i wouldn’t remember cause i need it only occasionally, and life-things like checklists for moving to another place or getting a new car. Whenever i search the internet for a solution to a problem and it takes longer than a few minutes to find the solution, i add it to the wiki so next time i search it again i know exactly where to find it fast. For me this was such a life changer and time saver (in the long run), cause before i had those infos in various text files and couldn’t find the information when i needed it.
Then a password manager is also a must have. I use KeepassXC, synced via Nextcloud to my phone and tablet, with a Yubikey for 2FA. I have way over 300 passwords in there. It makes it so easy to get a long and unique password for every site, that’s so important now that so many user/password combinations are leaked from hacked sites, cause i know a leaked password doesn’t give access to any other site. And KeepassXC can also store notes (like how to log in or how long a premium account lasts) and files (i.e. a geli key for the old zfs geli encryption) and it can even unlock ssh keys.
And third is a document management system. I chose paperless-ng cause it has OCR, a good way to automatically tag documents and good search filters to find documents easy. Before i had just placed my documents on my desk, then i had to clean up cause someone visited and then i would just throw them i a big bag. When i needed a document i couldn’t find it or searched for up to 1-2 hours. Now i get most documents in digital form (when they come via mail they get automatically imported), and the few ones i still get in paper are scanned periodically. So whenever i need a document i find it now in less than a minute.
And the last thing is an RSS reader, at least in tt-rss you can just star an article and it will never get automatically deleted (you could it even set it up to never delete anything but the database might get pretty big and slow). For RSS feeds that include the whole content of an article (some sadly only do headlines or a short introduction) this is a good way to save them practically forever.
And it’s a HUGE timesaver if you want to get the latest news from many sites.
For sites that don’t support RSS (sadly more and more, especially those social media ones) there is rss-bridge which is really good at parsing a website and generating a rss feed out of it, and it supports adding your own bridges for sites that aren’t supported natively.
Pro tip to track github repos: add /.atom to the url of the release or commit site of a project.
Some mentioned calibre here. As i left all my books at my parents house when i moved out, i have all books stored as ebook or pdf. I use calibre-web (instead of installing applications locally i try to run as may things as possible via docker on my server and access it via browser, so i can access them also remotely), but i haven’t found a good way to connect my e-reader (Kobo Aura HD) to it via wifi. The 3rd party reader app koreader can connect to calibre-web but the search feature doesn’t work well and i think there’s no way to sync read progress or notes. So i tend to use the webbrowser of my e-reader to access calibre-web to download a new ebook it hasn’t already stored locally.
But calibre-web just uses the default calibre database, so i could always just run calibre on my pc and sync it to the ebook via usb, but i haven’t done that for years. And i also don’t read that many books so i haven’t invested that much time into my calibre setup yet.