Jitter is a just in time image transformation plugin for Craft CMS with an API based on Imgix. It currently supports local storage or AWS S3 and requires ImageMagick.
This plugin was created to be a simple and free alternative to an Imgix style service. It does not and will not have all the bells and whistles that other paid services or plugins offer. If you need something a bit more advanced besides basic image transformations I suggest you select one of the paid plugins or services.