Do you want feedback?

Yes. I really appreciate feedback from people, regardless whether it is criticism, new ideas, bugfixes or just a general heads-up. Don't hesitate to send me an email at peter@cs.unisa.edu.au. I'm also reachable on #xorg-devel most days (Adelaide time) for architectural discussions. Ping user 'whot'.

Is MPX an extension for X?

No. MPX is deeply integrated into the source and the main part of X Input Extension v. 2.0. You cannot simply install it as an extension, you need an up-to-date X server.

Does it run under Windows/Mac OS X

No. Although there is a version of X for Windows but it does not quite work like X under *nix, Modifying it to accomodate MPX would be possible but the underlying windowing system still only supports one single pointer, so there's no point.

How do I develop programs with MPX?

Use the X Input extension instead of the core protocol for input events.

Does MPX have support for multiple keyboards?

Yes. Mice and keyboards can be hotplugged too.

What are the limitations?

Any legacy application that was designed for a single user only will have limitations. Simultaneous drag-and-drop within a window is not possible. The state to enable drag-and-drop is kept in the application (or library), using two mice at once will corrupt this state. This is a limitation of single-user applications that cannot be changed without modifying the application itself.Additionally, the X Protocol does not allow to specify devices on GrabPointer or QueryPointer requests. MPX has to guess which pointer to use. In some cases, this can be a semantically wrong choice.