Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
Redis - Redis is an open source in-memory data structure project implementing a distributed, in-memory key-value database with optional durability.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
NeDB - The JavaScript Database, for Node.js, nw.js, electron and the browser - louischatriot/nedb
Better Uptime - We call you when your website goes down
SQLite - SQLite Home Page