You can write a Rundeck Workflow Step Plugin in almost any scripting language. Since Python is a popular language inside many Operations organizations, it shouldn't come as a surprise that Python is also a popular choice for writing Rundeck plugins. In this short video, Alex Honor gives a walkthrough of a Step Plugin written in Python. This particular plugin wraps the AWS S3 CLI tool to provide a more user friendly experience within Rundeck.
The Github project for the plugin shown in this video can be found here: https://github.com/rundeck-plugins/aws-s3-steps