Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.

OpenXava - OpenXava is a Web Java Framework for Rapid Development of Enterprise Applications.

Eventbrite - Discover Great Events or Create Your Own & Sell Tickets

jHipster - JHipster is a development platform to quickly generate, develop, & deploy modern web applications & microservice architectures.

Bigtent - BigTent is a web-based organization and communication portal for groups.

Spring Framework - The Spring Framework provides a comprehensive programming and configuration model for modern Java-based enterprise applications - on any kind of deployment platform.