Erlang/Tk is the standard GUI toolkit for Erlang developers.
Some things Erlang promotes that you can try in Tcl... Erlang Idioms for Tcl
etclface - a Tcl extension that will allow software written in Tcl and Erlang to communicate using the Erlang/OTP interface, erl_interface.
Some of the aims of the Tcl extension are:
portcl -- helps create Erlang ports based on Tcl scripts. An Erlang port is a non-Erlang external program (or linked driver) that appears to the Erlang processes as another process and can communicate with these processes via the message passing mechanisms.
OTPCL (Open Telecom Platform Command Language) - Interpreter for a Tcl-like language written in Erlang.