http://www.ossat.org/

"The Open Source Show And Tell (#OSSAT) is a free event taking place roughly twice a year - a chance for fans of open source, open standards and open data to come and show what they've been up to. The next OSSAT is scheduled to start at 6.30pm on Wednesday 14th April. Entry is free, and we ask that you register via the event page on Upcoming. It's not compulsory, but does give us a nice idea of numbers!