QuickFIX
The original QuickFIX implementation in C++. The Java QuickFIX/J is based on this implementation and is compatible with the QuickFIX API.
HermesJMS
HermesJMS is a great open source JMS monitoring tool with additional features useful for developing JMS-based applications. It uses QuickFIX/J to provide a nicely formatted representation of FIX messages sent through JMS. It also support playback of FIX messages.
Log4FIX
A FIX log tool based on QuickFIX/J and developed by OCI. I don't have all the details yet about the location of the project but I'll update this entry as soon as I know (Steve).