You may be aware of Joomla 1.6 being out because of all the buzz and excitement happening around the Joomlasphere recently, but have you heard of Nooku Server?
Nooku Server is a Joomla! 1.5 based distribution. However, Nooku Server has been heavily refactored to remove legacy and other rarely used code and unnecesary bloat that currently haunts joomla. Nooku Server therefore provides better caching, faster performance, lighter footprint, improved security and a new admin backend.
Nooku Framework, the rapid extension development framework for Joomla is also part of Nooku Server. The Nooku framework powers amazing Joomla! components like NinjaBoard Forum (as used on this website) and the Anahita Social Engine.