This is a simple rqt-based ROS GUI for visualizing graphviz dotcode published over a ROS std_msgs/String topic.

First, open the rqt_dot GUI:

rosrun rqt_dot rqt_dot

Second, publish some dotcode from somewhere, like the command line:

rostopic pub -r 1 /dotcode std_msgs/String "data: digraph foo { a; b; a -> b; }"

Third, subscribe to a ROS topic by entering it by name and clicking the Subscribe button, and see the result:

You can stop updates by clicking again on the Subscribe button.