NewRelic Offers Free Rails Monitoring, Adds New Features
Now NewRelic has made RPM Lite available free of charge - that includes the Rails plugin and the hosted service that collects the data and the Real-Time Dashboard. There's no limit on how many Rails applications can be monitored with RPM Lite. More details are available in the RPM Lite press release.
The commercial versions of RPM are available in Bronze, Silver or Gold levels - each level adds another set of features. The features include Transaction Tracing (allows to drill down into the details of a transaction, down to the SQL), Error Tracking (classifies errors), Automatic Incident Detection (uses statistical analysis to see if sensor data deviates from a normal values), Customizable reports, and much more (complete list is available on the NewRelic website).
Currently Rails is the only supported web framework - with support for Mongrel, Thin, Litespeed, Passenger (mod_rails), and JRuby/Glassfish.