PatientOS
http://www.patientos.org
(an open source healthcare information system
Free under the GPL license)

PatientOS is a free clinical information management system for hospitals and healthcare practitioners. Pharmacy, the laboratory, registration and other departments will be able to automate many processes when version 1.0 is released October 31st, 2008. A physician practice version will be released March 31st, 2008.

Version 0.15 of PatientOS adds appointment scheduling in preparation for the EMR release for physician practices. The software can now be installed and running in minutes with a broadband internet connection.

Watch the installation and demonstration videos
http://www.patientos.org/software/video.html