Fldigi is a modem program which supports most of the digital modes used by ham radio operators today. You can also use the program for calibrating your sound card to WWV or doing a frequency measurement test. The program also comes with a CW decoder. fldigi is written with the help of the Fast Light Toolkit X GUI. Fldigi is a fast moving project many added features with each update. Flarq is a file transfer application that is based on the ARQ specification developed by Paul Schmidt, K9PS. It is capable of transmitting and receiving frames of ARQ data via fldigi. The fldigi-shell program controls fldigi over HTTP via XML-encoded remote procedure calls . It can call any XML-RPC method exported by fldigi, and also defines some useful commands of its own.