PassingPix.com
It can also log all tunnelled packets for easier debugging of networking applications.
Screenshot on Windows

Configuration sample

To set up a pipe on the local computer that listens on port 12345 and relays the UDP packets to port 23456 with 10% packet loss and a random latency between 50–200ms, the configuration looks like this:
Pipes = { MyRelay = { listen = ":12345", remote = "localhost:23456", drop = 0.1, minLag = 50, maxLag = 200 } }
More about the configuration can be found in the included file config.sample.lua.

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  • Mac OS X
    • 10.5 or newer
    • Works on PowerPC, but not officially supported
  • FreeBSD
    • [x11/libX11] X11 client-side library (not when using -noGUI)
  • Linux
    • [libx11-6] X11 client-side library (not when using -noGUI)
  • Windows
    • XP SP2 or newer (incl. Vista and 7)