Which aspects of your robot do you want to monitor? Are you looking for something like
rviz for web or a dashboard approach like
rqt, e.g. for plotting values?
If you are dealing with an industrial robot arm you might have a look at Rosvita (Videos) which is currently in beta.
Rosvita has a JS front-end that includes a 3D WorldView (visualization similar ro rviz) and a heart-beat based system status monitor (see package xamla_sysmon at github). The system monitor ensures that criticial components are responding (e.g. robot moves are disallowed when a gripper is not ready in order to prevent crashes).
[My opinion is biased since I am a member of the Rosvita dev team.]