Multi-pointer X (MPX) is a modification to the existing X.Org implementation of the X Window System. MPX provides multiple independent pointers (mouse cursors) at the windowing system level. These cursors are all connected to one computer. Unlike many other multi-pointer applications and toolkits, MPX allows many existing X Window applications to run unmodified, whilst still providing additional input features. For instance, multiple users can simultaneously operate different applications at the same time. Some applications do not work as expected due to limitations in the toolkits they use. The limitations are caused by the assumption that only one pointer exists.
Combined with the proof of concept window manager MPWM, MPX provides extended features such as simultaneous movement or resizing of application windows, per cursor annotation over top of an application and restricted input support (floor control). Applications that are aware of the extra cursors are also able to make use of them, such as two handed drawing.
Peter has since left the WCL but continues working on MPX and XOrg. You can find his blog at: http://who-t.blogspot.com/