Open Source Summit is the leading conference for developers, architects and other technologists – as well as open source community and industry leaders – to collaborate, share information, learn about the latest technologies and gain a competitive advantage by using innovative open solutions.
The 2019 edition takes place on Lyon, France on October 28 - 30, 2019.
Thanks for sharing the above event. I wanted to add that the Linux Foundation organizes many events around Europe related to different open source topics. Here is the list of events https://events.linuxfoundation.org/. Open Source Summit is also listed there.