Kolibri can be used on a variety of servers, with the RACHEL being one option. For context on the different types of servers that Kolibri can run on, including the RACHEL, take a look at Learning Equality’s hardware guide (being updated on an ongoing basis).
For more information on how Kolibri and RACHEL are different, I’ll refer you to an existing thread for more information.
Are you currently using Kolibri on a RACHEL device? If yes, which version are you using?