I'n not aware of an existing system that does this. TFS has a well documented client object model, so it should be relatively easy to do a one-way export to TFS. For more "automatic" syncs you can look at the TFS Integration Platform.
For publishing changes from TFS back to Salesforce, you could look at the same TFS Integration Platform, or do a server side integration through an ISubscriber plugin in-process in the TFS server or registering a SOAP event for a more decoupled solution.
I do not have any knowledge about the Salesforce api model, but I suppose that, it being a cloud product, they provide a webservice or a REST API which you can talk to.