Open Source X.500 Directory Projects?

DangerTenor asks: "The United States Government is standing up a Bridge Certificate Authority to enable PKI Interoperability between different agencies (gov't and non-gov't). The PKI currently relies on the use of either meta-directory products or X.500 DSP Chaining in order to pass certificates and CRLs between directories. OpenLDAP doesn't fit the bill because it doesn't support chaining. Does anyone know of open source projects focused on full X.500 directory implementation, or on meta-directory capabilities?"