Pidgin. Consume soo little memory in comparison to other chat applications. Is really fast, just try start and scroll history in a chat conversation. But it looks ugly.

Hey what about Kodi?

I don't 100% understand LPPL, but I believe it qualifies under open source, but regardless if it's open source or not, LaTeX > Word and I will die on this hill.

I use Gimp and Krita, ShareX also with the complementary Extension, integrated with FileCoffee, old but gold VLC media player, PicView image viewer/editor (IMO best alternative to IrfanView), ProtonVPN (yes, it's OpenSource), Crow Translate, FreeTube, Portmaster, Cherry Tree editor, apart of some games (The Dark Mod, Armagetron Advanced, Scorched 3D, and some more)

Are we allowed FOSS alternatives to common FOSS apps lol? In which case, I'm saying NeoStore > F-Droid.

Also, separately, Zotero > all commercial reference manages and increasingly over PDF readers too.

Feeder, a RSS reader for Android. It has great UI, is fast at finding and parsing .xml from a link and has a comfortable reading experience. It has basicslly replaced social media for me besides the fediverse. The only thing I wish it had was more customizability. Being able to install Nord theme on it would be great.

Let's be honest though, the Android app for jellyfin is so so buggy. My partner can't even use it because there are certain orders of starting a video, casting, closing the app, reopening to starting subtitles, recasting, just to get it working