Although I am not one of the founders of the Magento Stammtisch Rhein-Main, I have been a co-organizer for a long time.
The Magento Stammtisch Rhein-Main is an established part of the Magento community in Germany.
We have now organized more than 40 meetups.
How to Take Part
We have a Meetup page where you can find all upcoming dates: https://www.meetup.com/de-DE/magento-stammtisch-rhein-main/
Participation is free. Food and drinks are usually well provided for. Just come along.