Ethereum Push Notification Service - Protocol for incentivized, blockchain based notifications.
Zingo - Zingo is a communication app by Buzz Group Limited through which you can connect with a large community of other bright minds by engaging in live chat with them.
Blockbutler - Real-time transaction notifications for the blockchain
Bazoocam - Bazoocam is a popular chat website that rapidly connects you with strangers to chat.
Notif.me SDK - A Node.js lib to send all your transactional notifications
FriendZone - Make new friends based on your interests and hobbies