The latest stable Rivet release may be downloaded from the links provided at this page:

http://www.apache.org/dyn/closer.cgi/tcl/rivet

Apache Rivet is actively developed - you can always get the most recent version from SVN.

svn co http://svn.apache.org/repos/asf/tcl/rivet/trunk rivet

In addition, for your convenience, snapshots of the CVS tree are available here: http://cvs.apache.org/snapshots/tcl-rivet/