Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Qiqqa - Qiqqa is a free research and reference management software. It can be used in many organizational projects from the academic to the personal to the business endeavor. Read more about Qiqqa.
Calendify - Calendify is an event community where you can share, publish, and subscribe to event calendars. It helps you to stay informed about what you are interested in and what is yet to come.
JabRef - Graphical Java application for managing bibtex (. bib) databases.JabRef · JabRef Help · JabRef | Blog · OpenOffice/LibreOffice .