Windows 7

Below is a screenshot from a Windows 7 desktop accessing 3 applications on various other machines:

• Calculator running on a Linux machine, displayed via xpra
• System Monitor is coming from the same machine, but forwarded via SSH
• Epiphany is running on another machine and is forwarded via NX, the control window for this session is also shown

Windows XP

Below is a screenshot from a Windows XP desktop accessing a very large start menu located on a Linux server.
Another window is already running gedit on that server:

Linux

An Ubuntu desktop preparing to send the open gedit session to the XP_Pro user.

Mac OS X

A Mac OS X desktop running the Galeon web browser and Baobab disk usage analyser on a Linux machine nearby...

FreeBSD

A FreeBSD desktop showing the system start application menu, a Log File Viewer is already running locally.