Why does the invitation message of Design Manager refer to Rational Team Concert?

I can't see your picture but I believe that's a little of our RTC historical roots showing thru there.  The default team invitation contains that information.  There is currently no way to easily customize it.  We do provide an extension point that allows that to be customized by the application but that was more of a stop gap mechanism.  There is workitem Allow invitation content to be define in invitation templates (58809)  that tracks the better solution to it.

Don
Jazz Process Team