Cross platform multi-monitor multi-os support

 I have a couple old laptops lying around and always would've like to convert that dusty hardware into something I can use everyday.
Use these laptops as external monitors through software, no hardware hacking.
Speed can be a perk but, I'm just looking for the ability first.  So far I have not found a reliable solution.  The technology is there and currently exists as evident below but, the initiative has not advanced.

Why I am not the only one that want's this and concludes the precise reasoning of why this should be implemented: http://www.raspberrypi.org/phpBB3/viewtopic.php?f=41&t=12100&p=453357#p453357

Collected information:
displaylink - usb monitor support (would be awesome if these plug-n-play monitors like the 16" AOC usb-powered one worked the same way as another laptop connected by usb with a display driver that emulates a monitor)

xdmx - successful implementation of Windows Linux OSX multimonitor multisystem (very buggy, not very reliable, uses ssh over network, uses cygwin as an emulator for an x terminal, uses only x server for display output, no longer maintained as of 2004)

maxivista/zonescreen - the only implementation that I know of the successfully displays multiple screens over tcp/ip

piwall - libav based projection of imagery over 9 different monitors over the network using a player capable of projecting an image over multiple monitors at the server end.

Mobile Device Display - iDisplay, AirDisplay, for ios

Open Source monitor emulation:
http://www.ashokraja.me/tips/How-to-enable-dual-or-multi-monitor-support-in-Oracle-Virtual-Box

Best case scenario - open-source zero-conf cross-platform monitor detection over any udp-capable medium (cat5, wifi, bluetooth, etc...).

Open source working monitor support:
http://www.spice-space.org/home.html

New best case scenario: avahi serviced monitor detection using spice for windows and X for linux distros.  Server can only be run on linux.  Needs functionality to use windows as the server or implement a p2p instead of a server/client relationship.  Events would be transported over spice but interpreted by synergy.