Some foss games I can recommend are Battle for Wesnoth and Endless Sky.

sshfs

Seriously, it will change your life.

OpenTTD

LineageOS

Qbittorrent and LibreOffice

Synfig, very capable animation software.

@Sigmatank
Open source projects that are best-in-class, rather than imitators if commercial software

RStudio: just an everything box for software development in R, version-controlled website creation, and scientific publishing via Quarto.

Zotero: open-source, shareable citation management.

Joplin, a Markdown-based Evernote that let's you self-host your private notebook instead of giving it to a corporation to hols onto.

VLC: the video player that plays everything.

Yunohost! If you want to get started self-hosting some services, check out Yunohost. It's super easy to setup and run, active development and community, and just awesome. I found it so much easier than docker-based projects. I used to have it running on an old eeepc netbook, but now I have a dedicated tower server for it.

Micromath plus is a great graphic calculator app for android.

Oobabooga Textgen Webui - because offline open source AI is the biggest force multiplier and most powerful game changer in the last 20 years. It will reshape everything in the next couple of years. This will be bigger than the revolution of capacitive touch screens. Oobabooga is easy, and it makes playing with AI easy even if you don't have the best hardware. Get it on github, then go to Hugging Face for models. Look for prequantized models by The Bloke, read the model card. His models tell you the minimum requirements and what you need to do.

Equalizer APO + Peace equalizer (as the interface) + AutoEq (for the automatic equalization).

It allows to change do advanced and automatic equalization on audio devices, being audio outputs or inputs as mics.

AutoEq is the automatic part. It is more focused on Headphones/earbuds/iems presets. It's an automatic tool trying to equalize measured (by a compatible reviewer source, which is already in the database) headset to match the target the user wants, Then export a file for the software someone uses (peace for example).

As a common preset, the harman over-ear 2018/in-ear (depending on the device) is pretty good, but other presets are available too.

If you have an always on compute: Syncthing. Think google drive or Dropbox but with as many different folders and devices as you want.

If you're already on linux: KDE connect, even if you're not on KDE. Neat little pocket knife of ways to connect to your computer from your phone.

Cherrytree note app, Desktop
https://www.giuspen.com/cherrytree/