Originally I wanted to kickoff this topic with info on www.programmakwaliteitvanzorg.nl
A webapp for gathering research data on Alzheimers' patients and their caregivers. It ran on PF 4 and was upgraded over the years without problems to PF 6. In 4 years it gathered more than 10.000 questionnaires that were anonymized and sent to a national research institute. Findings contributed significantly to the treatment protocol and the role of caregivers in dealing with this disease.
Unfortunately the customer I made it for took it offline last year.
Currently I don't develop for a living anymore and my hobby project HeadStart I sometime use to quickly make a POC or just for fun. It's a template application with some out of the box features that can be hooked to a DB and can easily be expanded or taylored: https://github.com/httpeter/HeadStart