draw.io - Online diagramming application
MicroDicom - DICOM viewer. MicroDicom is a free DICOM viewer. Export to the most common picture formats, movie, clipboard. It is equipped with most common tools for manipulation of DICOM images.
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Horos - A free, open source 64-bit DICOM medical image viewer
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Weasis - Weasis is a multipurpose standalone and web-based DICOM viewer.