Wimpiggy is a library for writing EWMH-compliant, compositing window managers using Python and GTK+. The goal is to make writing a window manager as easy as writing a PyGTK application. This library can be used to build a trivial, working window manager in only about 40 lines of code.
X Persistent Remote Applications (xpra) is "screen for X". It lets you run applications remotely (like ordinary X or VNC), but unlike ordinary X, these applications are "persistent" if you lose your connection, or even if you want to switch to another computer. Also unlike VNC, they are ordinary applications on your desktop managed by your window manager, not trapped in a box.