Synthea is a Synthetic Patient Population Simulator. The goal is to output synthetic, realistic (but not real), patient data and associated health records in a variety of formats.
Nice offline tool to generate synthetic patient data..
The Australian government published a de-identified open health data set in the past, which contained the patient data of a subset of the Australian population. – The de-identification process involved not just stripping direct identifiers, but also adding some inaccuracies to the data set. However, the data set was still at the person-level.
Researchers have been able to successfully re-identify some patients.