The Lotus Notes system was one of the first to make replication a central component of its design, which has been one of the main reasons for its success.

PeerDirect
Home page for PeerDirect, developer of integrated network solutions. This site highlights their PeerDirect product, a heterogeneous replication solution for ODBC-accessible databases.

Troubleshooting Replication Problems
This replication troubleshooting checklist is the first resource you should consult when attempting to diagnose and solve replication-related issues.

PowerSync synchronization, replication & backup software for Windows.
PowerSync provides automatic file synchronization, replication, backup, and remote mirroring for Windows 3.1, 95 and NT. PowerSync keeps your data up-to-date and protected. It comes in a single user version and a Server-to-Server multi-user version.