**Logging** is a flexible logging library for use in Ruby programs based on the design of Java's log4j library. It features a hierarchical logging system, custom level names, multiple output destinations per log event, custom formatting, and more.
Fluentd is an open source data collector designed to scale and simplify log management. It can collect, process and ship many kinds of data in near real-time.
Tame Rails' multi-line logging into a single line per request