APCu is userland caching: APC stripped of opcode caching in preparation
for the deployment of Zend OPcache as the primary solution to opcode
caching in future versions of PHP.

APCu has a revised and simplified codebase, by the time the PECL release
is available, every part of APCu being used will have received review and
where necessary or appropriate, changes.

Simplifying and documenting the API of APCu completely removes the barrier
to maintenance and development of APCu in the future, and additionally allows
us to make optimizations not possible previously because of APC's inherent
complexity.

APCu only supports userland caching (and dumping) of variables, providing an
upgrade path for the future. When O+ takes over, many will be tempted to use
3rd party solutions to userland caching, possibly even distributed solutions;
this would be a grave error. The tried and tested APC codebase provides far
superior support for local storage of PHP variables.