Unorganized list of tools, that I use. This is not a complete list, most common things are omitted here.

• OS: Debian GNU/Linux (wheezy, aka testing suite)
• Mail:
  • mutt curses MUA
  • procmail MTA
  • fetchmail mail fetcher
  • spamprobe mail filter
• mcabber curses jabber client
• htop curses process monitor
• vim curses text editor
• awesome X window manager
• cmake build system
• mercurial distributed version control system
• lftp FTP client
• lua embeddable programming language
• GNU screen terminal multiplexor
• rxvt-unicode X terminal emulator (in daemon-client mode)
• rsync file synchronization utility
• transmission bittorrent client daemon
• rtorrent curses bittorrent client
• Media:
  • mplayer2 video player
  • mpd music player daemon
  • ncmpcpp curses mpd client
  • feh image viewer
• lighttpd lightweight web server
• prosody lightweight jabber server
• scim input method
• op flexible replacement for sudo
• schroot configurable chrooting tool
• elinks curses web browser
• bins static picture gallery generator
• ikiwiki wiki compiler
• timidity++ midi player
• strace system call tracer
• openvpn vpn client/server
• qemu machine emulator
• xpdf pdf viewer
• wodim optical disk burner (though, k3b is also great thing)
• cdparanoia audio cd ripper