Fldigi is a free and OSS multiplatform software for use digimodes with a soundcard or an external modem/soundcard. I use fldigi with a SignaLink USB.
You can download the source of fldigi here
Most Linux distributions contains a ready build version of fldigi. But mostly this versions are old, so it would be better to build your own version from the source. This is quite simple, I have wrote a small HowTo.
To use fldigi within CQRLOG you find a HowTo here.
sudo apt-get build-dep fldigi
After that, run again ./configure and make.