Many of us in the field have come across heterogeneous source control environments within the same organization. Some organizations, having multiple source control systems, wish to have some way of synchronizing TFS with their other systems. I've seen this when development teams who are used to the Microsoft development tools tend to prefer Team Foundation Sever and sometimes operations teams, who are responsible for deploying and maintaining the software produced internally maintain a portfolio of versions of the software in other control systems, like ClearCase for instance.
The TFS Migration and Synchronization Toolkit allows developers to build custom tools that provide migration and synchronization capabilities with other version control systems.
There's a new version of this toolkit available in Codeplex. This release includes enhanced support for the migration of branches and merges.