They suffered a server crash a few months ago, but they are now back online and still for free. Pay them a visit at least www.xacars.net.
“After a big crash on our server at the beginning of this year we finally managed to reopen our homepage together with all the documentation available on www.xacars.net.
This means that all users and all administrators of VAs using the only flight tracking software available for MSFS AND XPlane on all available platforms (Win, OSX, Linux), will have a common place to find information about XAcars and its setup again.
Our testsystem is open again too, so if you want to try XAcars without setting up a server first, you have the opportunity again! And yes, all that is still for free and will always be!
XAcars Development Team”