This is the third alpha release of the new 2.4 series of LIMB which fixes pretty good amount of bugs and adds some new features.
Here's the list of the most noticeable changes:
new more flexible full page cache subsystem
experimental events infrastructure added(instead of old status mechanism)
mysql db driver sets connection charset if it was specified
WACT template constants support added(e.g. {MY_FOO_CONSTANT})
published status fixes(reverting 2.3.x behaviour)
using FCKEditor 2.1.1 instead of HTMLArea
further PHP-4.4.x+ compatibility fixes