This is the Couchbase engine, previously known as the membase engine. Initially, somewhat jokingly, it was called the "eventually persistent" engine. The name stuck, we think mostly because it's easy to say.

You will need a storage-engine capable memcached and its included headers.

The easiest way to do this if you don't want to install memcached from source would be to just create a source tree and reference it.

For example, assume you keep all of your projects in ~/prog/, you can do this:

cd ~/prog
git clone -b engine git://github.com/membase/memcached.git
cd memcached
git checkout engine
./config/autorun.sh
./configure
make

cd ~/prog
git clone git@github.com:membase/ep-engine.git
cd ep-engine
./config/autorun.sh
./configure --with-memcached=$HOME/prog/memcached
make

An example invocation using the ep engine from your dev tree and keeping the database in /tmp/ep.db looks like this:

~/prog/memcached/memcached -v -E ~/prog/ep-engine/.libs/ep.so \
    -e dbname=/tmp/ep.db

While historically ep-engine had used tags and branches to describe it's versions, it no longer does so. The versions of ep-engine are now defined by the Couchbase repo manifest which may be found at https://github.com/couchbase/manifest

You will no longer find a tag for various releases of Couchbase.