Judging the maturity of a Plone product is generally easy. Start with a product’s project page on Plone.org. The product page (visit http://plone.org/products/plone) may offer you a Current release and one or more Experimental releases . Anything marked as a current release should be stable on its tested Plone versions. If you need a release to work with an earlier version of Plone as compared to the ones supported by the current release, follow the List all releases link.
Releases in the experimental list will be marked as alpha, beta, or Release Candidate. These terms are well-defined: