W1HKJ Software FLDIGI repository of software/support

Fldigi is a modem program for most of the digital modes used by radio amateurs today: CW, PSK, MFSK, RTTY, Hell, DominoEX, Olivia, and Throb are all supported. It can help calibrate a sound card to a time signal and do frequency measurement tests.

Beginners’ Guide to Fldigi (w1hkj.com)