Orthanc is described as 'aims at providing a simple, yet powerful standalone DICOM server. It is designed to improve the DICOM flows in hospitals and to support research about the automated analysis of medical images' and is an app in the Sport & Health category. There are four alternatives to Orthanc for Windows, Linux, Mac, Online / Web-based and Self-Hosted solutions. The best alternative is ClearCanvas Team Edition. It's not free, so if you're looking for a free alternative, you could try ConQuest DICOM server or dcm4chee.
dcm4chee is an Image Manager/Image Archive (according to IHE). The application contains the DICOM, HL7 services and interfaces that are required to provide storage, retrieval, and workflow to a healthcare environment.