Startups and applications that use backbone.js

• http://torrent-notify.me/ - service for receiving notifications about new torrent downloads.
• PhotoSpot - "Find 10 differences game". Backbone was added on the later stage of the project.
• blossom.io - painless issue tracking
• Brunch Colors - A simple, addictive color-matching game that is hosted as a Couchapp
• Shortmail - Length limited email
• BitTorrent - Desktop torrent download client
• HALL.com - More than a chat room, the War Room is the future of team collaboration where co-workers communicate and work in one place. Real-time collaborative features include team chat, file sharing, notepads, and video conferencing.
• Zuberance Self-Service - Zuberance helps marketers identify and energize brand advocates and track the results via social marketing campaigns. The public facing component of the Self-Service app is written in Backbone.js fronting a service API written in Scala on MongoDB.
• Ispikit - A web application to help English learners train and assess their pronunciation online.The app is architectured on backbone.js with twitter bootstrap's UI components for the views.