The Restful APIs feature is in the On-Premises version and it is possible to use this feature to build e.g. server-server integration.
Full documentation of this feature can be found here.
The Restful APIs feature has no smaller possibilities than in the SaaS version. However, there is one difference between the versions.
The way to manage the API Secret. This difference is due to the fact that the On-Premises version uses a different dashboard for configuration management than the SaaS version.
Instructions on how to get the API secret in the On-Premises version can be found in the API secret section.