A paper describing VRPN was presented at the VRST 2001 conference. A reprint of the paper can be found here. A copy of the Powerpoint presentation can be found here. A Powerpoint presentation on the vrpn_Imager can be found here.
Roman Shulakov from the Computational Science section of the Faculty of Science at the University of Amsterdam has developed a VRPN client that acts as a trackd server. This is a VRCO 'trackd' alternative for all versions of CAVELib (through at least 6/7/2001) that enables them to work with all VRPN-supported trackers. See his page at http://staff.science.uva.nl/~rshulako/projects/mytrackd/ for more information (and for his commentary on VRPN). You're welcome to contact him if you are interested in a copy.
Wouter Wognum write a VR Juggler driver for the WiiMote and interfaced it with VRPN. He tells you how at http://www.xs4all.nl/~wognum/wii.
Chris VanderKnyff has made .NET bindings for VRPN. Now client apps can be written in C#, VB.NET, and a number of languages other than C++ and Java. More information is available here at the project web site: http://wwwx.cs.unc.edu/~chrisv/vrpnnet.
Kyle Johnsen from the University of Florida made a VRPN server for the motion sensor in the Emagin Z800 visor. He also made a set of camera-control applications that let you start capture from a number of cameras on multiple computers at the same time. His code is available from http://www.cise.ufl.edu/~kjohnsen/software.html.
Evan A. Suma from ICT described their middleware called the Flexible Action and Articulated Skeleton Toolkit (FAAST), which is free software to facilitate use of these depth sensors with VR applications and games. It includes a VRPN server to send data from a Microsoft Kinect, including the pose for each joint of a user.
There is a VRPN tracker for the ARToolkit available from Universidad de los Andes. Someone made a Youtube video showing it being used to control the Blender game engine.
Andrew Montag and Kevin Godby have created an Android application that displays data graphically. You can find it here.
Scott Redig at the University of Minnesota Duluth SIVE Lab wrote a VRPN Web app to let you control an application with VRPN from HTML5. He reports: "It uses a simple json config file to define what controls you want to have. When the executable is run it serves both the webserver (so computers, tablets, smartphones, etc. can connect), and the vrpn server so your application can connect. I was able to set up the config in a few minutes for a project, and provided control to my application from both my iPhone and a nearby computer running Chrome. It currently only has been built on windows, however it should be able to be built on other operating systems. The github project along with instructions on how to use it can be found at https://github.com/Laremere/vrpn-webapp and downloadable binaries can be found at https://github.com/Laremere/vrpn-webapp/releases."
Alexander Morosow ported the Android VRPN server from the Comp523 class to work in native Java. It is available at https://github.com/worosom/java_vrpn.