D-RATS is a free, easy to use, multi-platform program for data communications with D-STAR devices or through the Internet. You do not need a D-Star Radio to learn how to use D-Rats.
D-Rats download page has install files for 32bit and 64bit
Get started with D-RATS using this detailed information.
D-RATS Ratflector List
D-RATS Operating Guide
Introduction To D-Rats