The OpenACS Kernel, which handles system-wide necessities such as metadata, security, users and groups, subsites, and package management and deployment.

The OpenACS Core, which comprises all the other packages that ship with the kernel and are most frequently needed by users, such as templating, forums, and user registration/management. The packages tend to be developed and distributed with the kernel.

OpenACS Application packages, which typically provide user-level web services built on top of the Kernel and Core. Application packages are developed separately from the Kernel, and are typically released independently of it.