Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Edit Any Webpage - Edit any site on the fly - bookmarklet
Event Hunt - Startups and Tech Events Curated By Locals
EditMode - Update website texts in real-time and get a sharable link.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Iteration X - Iteration X allows teams to annotate and edit any live website or web app directly in Chrome.