A proprietary content management system (CMS) is built by or for the use of a specific company. Unlike open source software, a proprietary CMS doesn’t allow open access to the source code, though it may provide an open framework (or API) that allows for extensions to the system. A proprietary CMS will generally require a licensing fee, though this may vary. This type of CMS is most appropriate for a company that has very specific security needs, or simply wants a full service hosting plan. However, there are also some limitations to this type of system; it may restrict you in terms of functionality, updates to software and design, and be costly to implement such changes.