Well, I thought I would have completed this previously in this thread(pre emacs) but I had not. cusp of 2020 edition:

music: mpd + mpc/scripted[1]
video: mpv
volume control: ponymix/fallback pavucontrol to check things
file manager: emacs(dired)
terminal emulator: emacs(Mx shell)
text editor: emacs
mail client: gmail web client ?
image viewer: emacs or meh
torrent client: deluge -- been meaning to checkout [2]
screenshot: maim/slop + some wrapper functions [3]
system monitor: xst+htop -- but I have just learned of emacs' proced, and it looks nice.
multiplexer: emacs
shell: bash

[1] playlists via search terms: https://github.com/neeasade/dotfiles/blo.../bin/music
[2] https://github.com/skangas/mentor
[3] I keep a folder called 'Last_shot' where I track the last screenshot -- this lets me pin the folder for GTK/qt file selector dialogs so it's easy/mindless to get the most recent screenshot. On new screenshots, the last shot is moved to ~/Screenshots