Edit: Updated the page with some cleanup and better navigation. It can now be filtered by OS and GUI/CLI.
Making posts for individual apps tends to only make sense when there's some actually notable event that takes place, so I figured why not just make a page that lists most of the open source applications that I use? So here is that listing. The webpage version has a nice table of contents for at a glance viewing; below is the page translated to Markdown, powered by Markdownr:
Writing
Joplin (Notes)
Website • Source Code • Get from F-Droid
I haven't been using it for very long. I used to use Logseq, but I've been finding that the more document/page oriented style of note-taking works better in some cases.
LyX (Math & Documents)
LyX is, without a doubt the best writing program. That's probably an exaggeration, but I do really like LyX. It's great for math, and even generates HTML; the first version of this page was drafted in LyX.
Saber (Handwriting/Drawing)
Honestly, I don't use this that much, however it does come in handy for writing/drawing on PDFs and for quickly jotting down equations.
Reading
KOReader (PDF/Documents)
Website • Source Code • Get from F-Droid
KOReader has a fairly minimal interface, but is quite versatile. It supports a lot of different document formats (and can also be used as an image viewer).
Tachiyomi (Web Comics)
Not much to say, it reads comics. It even has xkcd.
App Management
App Manager
Website • Source Code • Get from F-Droid
It's rather aptly named.
Aurora Store (Google Play Store)
Website • Source Code • Get from F-Droid
Somewhat ironically, this is only useful for installing apps that aren't on this list. However, it does come in handy if you don't have the Google Play Store.
F-Droid (App Store)
The quintessential FOSS software center for Android.
Termux (Android Terminal)
Not all software is packaged for Termux, but those that are can be quite handy. For example, Lyx is in the main repositories, and Code-OSS is available in the Termux User Repository
Audio/Video
PipePipe (YouTube)
Source Code • Get from F-Droid
It plays video from YouTube. The non-YouTube services it supports are different, but for those who only use YouTube, the primary differentiator I use it for is the ability to view comment replies.
VLC (Video Player)
Website • Source Code • Get from F-Droid
ViMusic (YouTube Music)
Source Code • Get from F-Droid
A straightforward YouTube Music client. It supports offline playback, though there is no way to get songs cached apart from playing through them. It can also be somewhat feature-bare at times.
Internet
Fennec F-Droid / Firefox (Browser)
Website • Source Code • Get from F-Droid
The quintessential FOSS browser. Well, maybe Chromium is, except everyone and their aunt has made their own proprietary spinoff of that.... On Android in particular, support for addons is a big plus.
K-9 Mail (E-Mail)
Website • Source Code • Get from F-Droid
"Thunderbird for Android" shenanigans aside, it's a nice email client in its own right.
WG Tunnel (Wireguard)
Source Code • Get from F-Droid
It's a Wireguard client for Android. It is mostly quality-of-life features that make it nicer than the official Wireguard client, such as being able to put spaces in tunnel names, search in app exclusion, and being available on F-Droid.
Games
AAAAXY (Platformer)
Website • Source Code • Get from F-Droid
A "simple" platformer. I recommend just trying it and exploring how it works yourself.
Forkyz (Crossword Puzzles)
Source Code • Get from F-Droid
You can play crossword puzzles with this app.
Puzzles
Website • Source Code • Get from F-Droid
A description is obviated by the name; it is a puzzle collection. I'm just going to be blunt and say I don't like most of the puzzles, however there are a few that I do quite like, and I recommend giving each of the sub-games a go.
Shattered Pixel Dungeon
Website • Source Code • Get from F-Droid
A fun roguelike. I'm not very good at the whole "stay alive" bit.
Programming
Code-OSS (Editor)
It's VSCode, but without proprietary bits. Telemetry may still be enabled by default, however.
Nim (Language)
Nim is hands-down my favorite programming language. The documentation is admittedly not the greatest, but it combines a lot of interesting ideas, and it gives a lot of freedom in terms of programming style.
Files
gdu (Disk Usage)
It's basically ncdu but in Go. I find that it works better than ncdu on Android/Termux
Syncthing (File Sync)
Website • Source Code • Get from F-Droid
Technically it is intended for file syncing, but I ended up using it for backups for the sake of convenience.
Miscellaneous
Arity (Calculator)
Source Code • Get from F-Droid
It's a calculator. Note: There are two applications on F-Droid. One is “Arity,” the original version, and the other is “ArityCalc,” an updated fork (which is listed here)
Barcode Scanner
Source Code • Get from F-Droid
In addition to the obvious capability of scanning barcodes, it can scan and produce QR codes, Aztec codes, Data Matrix codes, and many types of barcode. Admittedly, there's not much to scan QR codes for, but one (bad?) way I use it is as a lazy way to send a short string to another device.
Bitwarden (Password Manager)
Website • Source Code • Get from F-Droid
It's a password manager.
Krita (Drawing)
Website • Source Code • Get from F-Droid
I must admit, I'm not much of an artist. However, it's pretty good for basic image editing.
Organic Maps
Website • Source Code • Get from F-Droid
Maps are based on OpenStreetMap and can be downloaded for offline usage.
PDF Doc Scan
Self-explanatorily, it scans documents.
Simple Gallery
Source Code • Get from F-Droid
It's a gallery app. Unfortunately, SimpleMobileTools has been acquired by ZipoApps. Although the F-Droid version will probably not be affected, it doesn't seem likely that they will remain maintained. Hopefully one of the forks will be successful.
Unexpected Keyboard
Quite a basic, no-nonsense keyboard. It can take some time to get used to the positioning of the symbols and how to swipe for them.
Thanks! I highly recommend making your own lists as well; there are many high-quality pieces of open source software that I would have never heard of had it not been recommended.