e-Lock PKI: A certificate issuance system that is integrated with CryptoAPI. [Free] (e-Lock)Entrust/PKI: A certificate issuance system for Windows NT, HP-UX, Solaris, and AIX. (Entrust)pyCA: Python software for running a certificate authority on UNIX. [Free / Open Source] (Michael Ströder)Red Hat Certificate System: Based on system acquired from Netscape. Supports deployment and maintenance of PKI solutions including the issue and revocation of digital certificates. [Red Hat Linux, Solaris]