Dogtag Certificate System is described as 'The Dogtag Certificate System is an enterprise-class open source Certificate Authority (CA). It supports all aspects of certificate lifecycle management, including key archival, OCSP and smartcard management, and much more'. There are nine alternatives to Dogtag Certificate System for a variety of platforms, including Windows, Self-Hosted solutions, Mac, Linux and Online / Web-based. The best alternative is xca - X Certificate and Key management, which is both free and Open Source. Other great apps like Dogtag Certificate System are EJBCA (Freemium, Open Source), VeriSign (Paid), OpenXPKI (Free, Open Source) and CertHat - Tools for Microsoft PKI (Paid).
X Certificate and Key management is an interface for managing asymetric keys like RSA or DSA. It is intended as a small CA for creation and signing certificates. It uses the OpenSSL library for the cryptographic operations.
PKI solution based on Microsoft AD CS (Active Directory Certificate Services) offers a affordable and powerful digital certificates environment, however sometimes it can be challenging to use without additional tools (3rd party utilities or scripts).