The current release is v1.01.00b02. It is a cleaned up version of the reverse engineered JAR with as much functionality as possible removed to make the code simpler. The code also has been moved to another package. You can download the release from the file releases page of JContractS.
At the same page you can also download the original JAR files (package icontract), the source code of the original JAR for JDK 1.2 which has been modified so it builds using a modern version of Java (package icontract2), and the JAR built from this source code (package icontract2).
The project page of JContractS at SourceForge.net