Aardvark Communications
   Solution which can replicate heterogeneously between various relational database platforms.
   http://www.aardvark.on.ca/pd/replicate.html

Database Replication
   DBMS Magazine article by Charles Thompson comparing three leading DBMS vendors' approaches to replication.
   http://www.dbmsmag.com/9705d15.html

Progress Software
   Offer Progress DataXtend RE, a data replication tool for online and offline use.
   http://www.progress.com/dataxtend/dataxtend_re/