Any medical image viewer that uses DICOM to access images over a network should be able to integrate with dcm4chee. This list includes commercial as well as open source applications. It is not inclusive of all DICOM workstations, so if you know of one that works with dcm4chee, add it to the list!

Free and/or Open Source

K-PACS is a great DICOM viewer which is pretty much a free replacement of eFilm.
If you're using a Mac, you really can't go wrong with the open source Osirix application. It is an extremely sophisticated, full featured application for viewing and manipulating medical images.
Aeskulap is a free DICOM reader for Linux that can Query/Fetch from a PACS system. I tested this with dcm4chee-2.10.13 running on a Linux-2.6.18 server and it worked - Evan
Clear Canvas Workstation is a free DICOM viewer for Windows that's open source and written in .NET. I've tested this with dcm4chee-2.13.6 running on WindowsXP.
Ambivu 3D Workstation is a fully functional free 3D workstation for PC and Mac that has been tested with dcm4chee.
Ginkgo CADx is an open source multiplatform DICOM workstation. It runs great in linux , windows and macosx, and has dicomization and CADx (computer aided diagnosis) capabilities.

Commercial

Merge eFilm has been a work horse in the stand-alone viewer market for years. Too bad it isn't free anymore!
MedDream is cost effective, ready to integrate and easy to use HTML5 zero-footprint DICOM Viewer. Try newest version of FDA cleared for diagnostic use and CE certified as a Class 2 medical device by SOFTNETA online demo here or download it easily.

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