Orphereus

Orphereus is a modular imageboard engine with a broad set of features: a flexible system of tags and filters, a pluggable architecture, memcached support for better performance, full-text search powered by the Sphinx engine, a private mode where invitation is required to join, AJAX, extended security, highly customizable appearance, an improved analogue of tripcodes, news and statistics modules, advanced administrative, a maintenance subsystem, internationalization, and much more.