What is Turpentine?
Turpentine is a Magento extension to improve Magento's compatibility with Varnish, a very-fast caching reverse-proxy. By default, Varnish doesn't cache requests with cookies and Magento sends the frontend cookie with every request causing a (near) zero hit-rate for Varnish's cache. Turpentine provides Varnish configuration files (VCLs) to work with Magento and modifies Magento's behaviour to significantly improve the cache hit rate.
Full Page Caching, with hole-punching via Varnish ESI and/or AJAX, even for logged in visitors
Configurable via standard Magento methods (Admin system configuration and layout XML), no manual editing of Varnish config required for most cases
Able to generate and apply new Varnish VCLs (configurations) on the fly, without restarting/changing Varnish's config files or flushing the cache
Blacklist requests from caching by URL or parameters (SID, store, etc)
Note: Turpentine is only compatible with Magento 1.
Configure cache TTL by URL and individual block's TTL
Supports multiple Varnish instances for clustered usage
Automatic cache clearing on actions (clearing product/catalog/cms page after saving)
Supports non-root Magento installs (i.e. putting Magento in /store/ instead of /) and multi-store/multi-site setups
Support for site-crawlers for cache warming, and includes a (basic) built-in site-crawler
SSL support through Pound or Nginx