For a long time, Tcl was referred to as Unix's best kept secret. It hides inside products from Cisco routers to EDA tools, and is the scripting tool for health information, computer security, engineering applications and more. It's the language running bakeries, oil rigs, broadcasting studios and cargo ships.
And most programmers don't even know it exists.
Within the Tcl Secret Society is the even more select secret society of the Tcl/Tk Conferences. There are two each year, one in Europe during the spring or summer and one in the US in the fall.