How to remote desktop a computer over internet [duplicate]
Solution 1:
Teamviewer. Cross platform. Easy to use. There is even a portable, no need to install, version.
Solution 2:
The VNC protocol allows you to see and control others desktops. Since it's a protocol there are different clients and servers. On of them is tighvnc http://www.tightvnc.com/ which is free and open source software. And multiplatform as well.