The Embeddable EJB 3.1 is a work in progress.
We did silently release an 1.0.0-Alpha1 which is compatible with AS 5.0.0.GA. I'm planning to do a 1.0.0-Alpha2 release which is compatible with EJB 3 1.0.0.
For more instructions on how to use: http://wiki.jboss.org/wiki/EJB31Embeddable.
The plan is to have an embeddable available to co-release with Enterprise Application Platform 5. This could be JBoss Embeddable or EJB 3 Embeddable. It depends a bit on how many standalone components will be available.