What's the difference between step-ca and Smallstep Certificate Manager?

Smallstep Certificate Manager is a commercial product built on step-ca. However, with Smallstep Certificate Manager, setup and maintenance are both UI driven and provide role-based administration from one central web interface.

Smallstep Certificate Manager is a commercial product built on step-ca. An important distinction is that with Smallstep Certificate Manager you have a website Dashboard that provides you with UI tools and quick-starts which make it much easier to set up and maintain.