Interested in a Website ?
An example for dentists can be found here: drdittmer.expandmade.com
This website does have just the basic functionality. Individual requirements like online appointments can be added any time.
Interested in a Webapplication ?
If you do have already a web space and you are looking for an individual web application which can grow with your requirements: https://invoice.expandmade.com
Interested in an ERP ?
If you are interested in an ERP system, checkout Dolibarr: https://demo.dolibarr.org/public/demo/