The Tokyo Linux User Group
I have been running the Tokyo Linux User Group for the last 13 years. The club was started in 1994. I was first involved in 2002.
We have an event once a month alternating between technical meetings were we have speakers and Nomikai's[1] (Japanese drinking party).
Its hard to say exactly how big the group is because we have a lot more users lurking on our mailing list then people attending any given event. Our events attract between 10-30 attendees, and they are mostly different people depending on the time and topic being discussed.
Open source software dramatically changed the way a lot of people used computers. A lot of open source software runs on Linux which made TLUG a great meeting place for a diverse group of people.