http://www.xcsoar.org/discover/2012/06/30/SkyLines_Live_Tracking.html

One major feature of XCSoar 6.4 will be SkyLines Live Tracking. I
would like to introduce you to it.

SkyLines implements a very light-weight tracking protocol that transmits only 48
bytes for each fix, opposed to hundreds of bytes for other protocols. It works
better when the connection is flaky (and it usually is in a glider!), because it
does not require a complicated handshake between client and server. It transmits
not only your position, but also altitude, speed, vario, engine noise level.

Due to these advantages, you can easily set the tracking interval to only a few
seconds, and make the word “live” in “live tracking” credible.

Thanks to Josh Cohn who will be testing this. I didn't have luck
with my Samsung Android phone using Gaggle.