What software can I use to do live screen-casting in linux?

Try ffmpeg with something like this:

ffmpeg -vcodec mpeg4 -r 10 -g 300 -vd x11:0,0 -s 1280x1024 http://localhost:8090/feed1.ffm

If it's not working right with the exact settings from the example, see the ffmpeg webpage and documentation for more details: ffmpeg.org

The Ubuntu Screencast Team uses gtk-recordmydesktop.

Open-source, works on all platforms, support streaming to popular services out of the box: https://obsproject.com/