Xebra is an open source, cross-platform, thin client and server for web-based distribution and clinical review of medical imaging results. Xebra is based on the latest open industry standards including JPEG2000, WADO and IHE XDS-I.
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iPath is providing a free and open platform for "case based collaboration", especially designed for medical applications (telemedicine, etc). The iPath-Server package provides a sort of medical BBS to discuss/consult cases online. Additional modules are available.