From the website:
FlightAware is a free flight tracker that will change what you think about live flight tracking and aviation data.
Long time Tcl'er Karl Lehenbauer is listed as one of the founding employees.
This interview with Karl [L1 ] mainly focuses on FlightAware's use of FreeBSD and PostgreSQL, but also touches on the use of Tcl. Much of the website seems to use Rivet, as pages have a suffix of .rvt
A success story from AMD's website reveals: The company, which successfully migrated to AMD64 in less than two weeks, is running FreeBSD, PostgreSQL and TCL (Tool Command Language), a popular development language for real-time applications, on 2P AMD Opteron™ Model 250 processors. [L2 ]
Wow, Tcl is a popular development language for real-time applications. ;-)