Rack::Cache is suitable as a quick drop-in component
to enable HTTP caching for Rack-based applications
that produce freshness (Expires, Cache-Control)
and/or validation (Last-Modified, ETag) information.

 * Standards-based (see RFC 2616 / Section 13).
 * Freshness/expiration based caching
 * Validation
 * Vary support
 * Portable: 100% Ruby / works with any Rack-enabled framework.
 * Disk, memcached, and heap memory storage backends.

WWW: http://tomayko.com/src/rack-cache/