Liberate
Liberate is a application developed by Netrix which makes it possible to use the explorer.exe on Zune HD. It also provides functionality to run OpenGL, DirectX and Windows Apps on Liberate.
Wi-Fi problem
In order to save battery, the Zune automatically disables its Wi-Fi connection after a few minutes. This causes problems when trying to run executables that utilzie Wi-Fi for extended periods of time, such as when using the Windows CE Remote debugging tools through Liberate.
Liberate has a somewhat working fix in RelayInput.exe, which simply pings google.com and yahoo.com every couple of minutes. However, this fix is only triggered when Liberate detects the Zune is online via ZDKCloud_IsConnected(), which nowadays always returns FALSE since it uses the now-offline Zune webservices as a litmus test for internet connectivity.
Current research on a permanent fix are here.