There's no explicit web page that lists the changes made, but the mailing list says:
* Complete refactoring of system into 63 modules organized into four subsystems.
* Complete redesign of the build system, with performance, maintainability, and extensibility improvements.
* Support for evolution in sensor data types.
* New Sensor Data Type: "Code Issue"
* New sensors for: PMD, Emma, FindBugs, Checkstyle, Subversion
* Stable releases and nightly builds are now binary distributions (30 MB rather than 180 MB)
* Improved property file design (hackystat.build.properties and hackystat.site.properties)
* CCCC sensor now works with standard version of CCCC.
* Hackystat is now Java5 compliant (backward compatible to JDK 1.4.2)
* Hackystat server now compatible with Tomcat 5.5
* Jira sensor works with SSL.
* Hackystat source repository now hosted using Subversion.
* And many more things, as documented in Jira here
You can download Hackystat at http://www.hackystat.org/.