QuestDB

QuestDB is an open source time-series database. It doesn't have any local groups, but there is a global community built around slack, the community forum, and occasional encounters at events. None of those are ideal places to manage logistics in case there is a group of folks who will happen to be at the same place same time and want to talk about QuestDB and the broader time-series database communities.

This DevRelish group seems to be a good place for that :)