Thaw - Meet people you should know, but don't
Ethereum Push Notification Service - Protocol for incentivized, blockchain based notifications.
TaskRabbit - TaskRabbit connects you to safe and reliable help in your neighborhood.
Blockbutler - Real-time transaction notifications for the blockchain
Penpal Café - Find a person you can share your observations with.
Notif.me SDK - A Node.js lib to send all your transactional notifications