This is the Narrow Band Emergency Messaging System.  It was developed by hams in Western PA where the hams are VERY active in EMCOMMS, particularly with the Red Cross.  This system consists of several programs which work together to provide EMCOMMS on both VHF/UHF and on HF.  The software is free.The main programs are:
  • fldigi - this is the main program for digital messaging.
  • flmsg - this provides message templates, including ARRL Radiogram, Red Cross Health & Welfare, FEMA, and many, many others.  This is a very useful program!
  • flwrap - this allows the computer to "wrap" a file you are sending with a checksum so the recipient knows the file was received intact.
The original files are available for many different operating systems, including Windows, Linux, and OS X.  You can download the latest versions these websites, Windows download or Linux download.
Once you've downloaded the programs, here is an
NBEMS Setup Guide on the web to help you get everything set up and working.  You may also download a PDF version of the Setup Guide.  Just about everyone, if you will follow the steps in the guide carefully, should be able to get fldigi working correctly. 

What's really special about these modes is you can operate them with NO hardware interface, using any radio and computer.  The modes do work better with a hardware interface, but you'll be surprised how much you can do with very little.

If you really want to get into detailed documentation, there is a wiki for fldigi here

Below are links to a couple of tutorials prepared by some of the hams in Western PA.  As fldigi is always being updated, keep in mind that there may be some differences between  your copy of fldigi and the version used in the tutorials.