The RanorexLibrary offers an integration of the Ranorex API into the Robot Test Automation Framework. This means, you can write Robot tests like you are used to, and use Ranorex functionality to automate GUIs independent of the underlying technology.
You can find a full documentation about the RanorexLibrary and how to use it in the Wiki.
Please note: You will still need valid Ranorex licenses to run the tests.