VLC - Video/Audio player, encoder, decoder etc.
Wine (on Linux) - for playing games especially
VSCode - Intelligent editor with good community support
Signal - Private messenger app
¹ it should be able to traverse NATs. I could deal with having to set up a main server. edit: typos
It's the most amazing piece of free software that we all use almost every day, regardless of the platform or browser you use. Web browsers across the board are an amazing piece of software that's been in development in one way, shape, or form since the early '90s. Thousands of people have worked on them or contributed code, and they provide access to the bounty of the internet for nothing. Show me something more inspiring than that.
The tooling is fantastic and getting better all the time.
- pi-hole - irssi - plex
openwrt: works on many devices and so impressively stable
xbmc/kodi: although I don't use it daily, it is a complex yet very functional piece of software
winamp: simple, easy, functional, light
go+liteide: simple, easy, no nonsense
nomachine: not open source, but good
Actually, that's my whole environment discounting libraries and utilities which include Julia, Scheme and C++.
On Emacs, I adore org, magit, notmuch, eshell, calc and dired.
Redis
PostgreSQL
VLC
Perl
GNU tools like grep, xargs, find etc.
PostgreSQL
Redis
Blender