Team Foundation Server always had a rich extensibility story. By using the Team Foundation Server object model you could change or extend almost every part to your needs. The only disadvantage of the TFS object model is that the only way to install it was to install VS or Team Explorer, both of which included a VS shell, Office extensions and a bunch of stuff that you really didn’t need to do basic programmability against a TFS server.
Good news! Last week Brian Harry announced that they released a stand-alone installer(as part of VS Update 1) that would just install the programmability components – making for a faster, smaller and less impactful install.
You can download the installer here: http://visualstudiogallery.msdn.microsoft.com/f30e5cc7-036e-449c-a541-d522299445aa