I worked on a Plone add-on to manage conferences. I already created such an add-on to run the LibreOffice conferences in Berlin (2012) and Milano (2013). But this add-on was build against a former version of Plone and Python 2. It used the Grok style which could have some side effects. Thus I decided to move away from Grok style for an upgrade / a new setup of the add-on.
I already moved all modules and active functions away from Grok and reordered the structure of the add-on. I added a new configuration panel to the administration page. I could also fix relations and the indexing. You could get the code from Github at: https://github.com/collective/collective.conferences.