A-Patch for Messenger (Hacking)

A-Patch for Windows Live Messenger & MSN Messenger is a small program that can completely transform messenger windows and behaviour. Among others it can remove advertisements (removes ads from all windows), add always-on-top button, remove buttons and much more.

A-Patch supports versions 7, 8 and 8.5beta of messenger.

Website: http://www.a-patch.org/
License: Freeware
Similar: Mess Patch @ http://www.mess.be/

TeamViewer (Network)

Teamviewer is a small utility that allows you to take control over a computer anywhere on the Internet, even through firewalls. Actually is a vnc client that requires only port 80 (http) to work.
(Edit: I' ve just heard about CrossLoop which looks like a free alternative to teamviewer)

Website: http://www.teamviewer.com/
License: Shareware
Similar programs: LogMeIn Hammachi (vpn over http), CrossLoop