Here is my list:

• pdf - pdftk
• images - imagemagickutilities
• audio/video - ffmpeg
• documents - libreoffice --headless mode, also pandoc
• download files - wget and curl, also ytdlp for youtube, reddit
• cloud storage - rclone

My friend was running firefox on linux mint, and it froze and he used xkill to kill firefox. But still it shows up in htop ps -aux. He tried to kill it multiple times but it didn't work. See the pictures for explanation. We had to kill power to shutdown, even systemd can't stop that process.