Platform: GNU/Linux

Security
- nmap
- iptables
- Nessus
- john

Networking
- Firefox
- X-Chat
- GAIM
- BitTorrent
- gFTP
- KTorrent
- Gtk-Gnutella
- YOU / apt-get / emerge (depending on distro)

Misc
- bash
- GEdit
- Xorg
- perl
- gcc
- GNOME
- xmms

I'm sure I forgot something, but I use all of those quite frequently. Also, sorry to bump such an old topic, but it's stickied, so I figured it'd be ok. :P