Monitor an app for errors

hello there

how can i monitor an app. what i need most is when and where error pages
were printed to user, such as RoR errors, database problems or such.

is there an instance problem that i can use avalaible to views or
helpers
???

There are a couple of plugins that provide notifications of errors via
email:

http://agilewebdevelopment.com/plugins/search?search=notification