Logs are metrics waiting to happen.

MOAR GRAPHITE DASHBOARDS

How to use syslog(3) to emit metrics and rsyslog for transport.

A combination StatsD, carbon-relay, and collectd-graphite-proxy.

Coda-style metrics in Ruby.

An awesomely comprehensive listing of monitoring interoperability tools.

Event grapher that performs not just predetermined mathematical transforms on input but arbitrary Ruby functions.

Stats from Rack apps. This can definitely be extended to do more, a la codahale/metrics and friends.

Perhaps the biggest revelation in reading the source, however, is that you can change a Ruby process' title by setting $0.

Arbitrarily organize a bunch of Graphite graphs.

DTrace for Linux. Ish.