Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Siteoly - The fastest way to build websites using Google Sheets
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Spreadsheet 2 Site - Generate beautiful list sites from your spreadsheets
Bigtent - BigTent is a web-based organization and communication portal for groups.
XCalSync - Automatically copy events between your calendars.