Anki (and AnkiDroid):

The gods of learning and studying with flashcards. You will never want another flashcard program, especially if you were still using Quizlet (so enshittified now...) because Anki uses SRS (spaced repetition system) which makes you review things right before your brain forgets it to reinforce the subject material.

Add-ons: Bread and butter of Anki, I use several to make beautiful automatic flashcards of reading material/videos/games when I study Japanese. There's an add-on for literally anything.

Cross platform: Free on desktop, cost $25 on iOS, and free on Android, although Ankidroid is an unofficial app. Still great though!

Cloud: Syncs your anki database across devices. If you don't use anki for a while, will delete from the cloud, but as long as you have your own local database intact, you can reupload again later.

Sharing Decks: If you don't feel like making your own decks, download ones that others shared for free.

Anki is used by language learners, college students, med students, etc. If you need to memorize it, use Anki.

Pandoc: A universal document converter allowing conversion among numerous markup formats including Markdown, LaTeX, HTML, and Word.

tmux: A terminal multiplexer that enables managing multiple terminal sessions within a single window, allowing detaching and reattaching sessions to keep programs running in the background.

OsmAnd, mobile app for navigation and maps. Offline, based on OSM, can do anything. I use it for checking out and bookmarking places, finding POIs and pubic transport stations, routing (especially for bike and foot), measuring distances, and so on. It can also show and record tracks, do car navigation, edit OSM points, and more stuff that I don't use. Pro/plus/full version free on FDroid

Zotero: a free and open-source reference management software to manage bibliographic data and related research materials, such as PDF and ePUB files.

Shattered pixel dungeon. Open source dungeob crawler roguelike. Extremely fun.

Immich is a photo/video hosting solution à la Google photos

Typst: A modern typesetting system designed for easy document creation with markup inspired by Markdown but more powerful and programmable.

rnote Rnote is an open-source vector-based drawing app for sketching, handwritten notes and to annotate documents and pictures. It is targeted at students, teachers and those who own a drawing tablet and provides features like Pdf and picture import and export, an infinite canvas and an adaptive UI for big and small screens.

FairEmail, email app for Android that has every feature I can imagine. Available on FDroid

Lemmy ^[1]^

PieFed: a link aggregator and forum platform built for the Fediverse, focusing on individual control, safety, decentralized power, and healthy community interactions, with features like reputation indicators and keyword filters to enhance user experience.

screen

a gnu until that let's you run a persistent session, even if you log off. log back in and reattach your screen and whatever you were doing is still running.

Copyparty turns almost any device into a file server with resumable uploads/downloads using any web browser

This post is a gold mine!

Czkawka: A free, fast, and open-source tool for finding and removing duplicate files, cleaning empty folders, and optimizing storage by content-based file comparison across multiple platforms.

Tenacity - a pre-enshitification fork of Audacity. An audio recorder and editor that does multi-track recording, effects and much more in a really simple UI.

Xournal++: A C++ handwriting note-taking software with PDF annotation support.

Flameshot: screenshotting tool with everything you would ever need for screenshots

Nicotine+: A lightweight, free, and open-source graphical client for the Soulseek peer-to-peer file-sharing network.

Helix Editor: A fast, post-modern text editor that combines modal editing and syntax awareness built in Rust for programmers.

Nuclear: A free, open-source music player that streams content from multiple free sources like YouTube, SoundCloud, and Bandcamp without ads or subscriptions.

Mullvad vpn, probably the best vpn imo

emacs, the text editor. it's so powerful and customizable that I feel listing any feature would do so many others a disservice

Comaps, navigation from openstreetmap

Audiobookshelf. Not exactly a "hidden" gem at this point, but I'm putting it here for today's lucky 10,000. Simply the best way to store and stream audiobooks. Does podcasts too, and ebooks, although there are better tools for those.

Zathura: A highly customizable, minimalist, and keyboard-driven document viewer supporting PDF, PostScript, and DjVu via plugins.

Pass: a terminal based standard unix password manager.

binary eye, OR code and barcode scanner with no ads

Portmaster, nowadays mandatory, monitor the traffic of all installed apps and even from the OS itself, blocking with a simple click all unwanted traffic, Inbuild DNS crypt with dynamic filterlists (customizable) blocking ads, trackers and unwanted crap from big companies. Optional SPN service (paid). Windows and Linux.

https://safing.io/

https://github.com/safing/portmaster

Breakout71

I could not believe I didn't find this fun free gem sooner. I'll let the description from F-Droid explain the details:

This is a roguelike twist on the original Breakout formula: The goal is to catch as many coins as possible during 7 levels. Coins appear when you break bricks. They fly around, bounce and roll, and you need to catch them with your paddle. At the end of the level, you get to pick upgrades. There are 50+ different upgrades that impact the gameplay in various ways. Many upgrades will impact your combo, that's the number of coins spawned for each brick broken. Your "combo" is displayed on your paddle. Your score is displayed in the top right corner of the screen. Oh, and don't miss the ball, you don't have extra lives.

Subsurface

I recently found out after creating Linux, Linus Torvalds wanted to make a good open source scuba dive log software. Today, it's probably one of the best, if not the best dive log programs out there and I recently used this myself on a recent dive and it's great.

FindMyDevice, a find my server with channels through sms, a self hostable server, notifications. This is one of my favorite android utilities.

Markor is a handy fast Android note taking app with Markdown and todo.txt support.

Since everything it creates are text files, it pairs well with various file syncing apps recommend in this thread.

zoxide: A smarter cd command. Supports all major shells.

This is such a handy tool, and the database can be queried for other tools too. Like project switchers or fzf for example.

simple-scan. Scans documents with zero fuss. Easy and intuitive which is important for software that is not used frequently.

agate and amfora, a server and client for the text-based "small web" protocol called Gemini. Allows to publish and read text, images and media in a really simple and accessible way.

(Works also great in a local file network to distribute media and docs).

I think android HealthConnect doesn't get enough notice as it is a kind of silent background service.

It is local, opt-in, and privacy respecting connection API for sharing data between fitness apps with fine control over what gets shared where. You can have the shittiest privacy-violating fitness app and it can't just steal all of the data from your smartwatch or whatever because you connect the two apps via a stupid cloud integration.

Dino: a modern open-source chat client (XMPP) for the desktop.

zellij: A modern terminal workspace and multiplexer focused on usability and extensibility, featuring configurable layouts and plugin support.

OsmAnd: This map application is popular enough that it probably doesn't need mentioning, but good golly is it a powerful tool. Great options for downloading maps and having them offline, and while the car navigation might be missing one or two key features that you'd expect from proprietary alternatives (like live traffic), the sheer amount of detail that has been crowdsourced is mindblowing. There are a wealth of trails and cycle routes, low level details like park benches, bridges, and lookout spots, and the various map profiles you can build are very customizable. I'm personally a huge fan of the trip recording plugin for tracking all my hikes, runs, bike rides, canoe trips, and even swims.