We are experimenting with other user interfaces, including ones based on speech and gesture recognition. Currently they only issue commands to VMD so instead of incorporating these programs directly into the code we have developed a simple mechanism to receive external text commands. It is based on the Tcl extension package, Tcl-DP, which adds commands to interface with standard socket communications. It allows other programs to send messages to VMD\ and be interpreted as if they originated from the keyboard. If the command returns information, that data is sent back to that calling process.
The external interface works by setting up VMD as a server for remote execution of a Tcl command (VMD is a Tcl-DP RPC server). Other processes can contact VMD by connecting to a port. The remote process sends a text command to VMD which interprets it and sends the result back to the remote process, which can do with it as it may.