Xpra is a multi-platform persistent remote display server and client for forwarding applications and desktop screens.
It gives you remote access to individual applications or full desktops. On X11, it is also known as 'screen for X11': it allows you to run programs, usually on a remote host, direct their display to your local machine, and then to disconnect from these programs and reconnect from the same or another machine, without losing any state. It can also be used to forward full desktops, from X11 servers, MS Windows, or Mac OS X. Xpra also allows forwarding of sound, clipboard and printing services.
With X11 programs, Xpra can be used "rootless" or "seamless": programs you run under it show up on your desktop as regular programs, managed by your regular window manager. Sessions can be accessed over SSH, or password protected over plain TCP sockets. Xpra is usable over reasonably slow links and does its best to adapt to changing network bandwidth constraints.