A simple, plugin-based system for monitoring systems on a small scale. The idea is to make it super fast to make plugins that either monitor something or send data about what monitor plugins said through another service. It's not intended to be a full-fledged monitoring application, just a "send me a push notification if x breaks" sort of deal.
I use it myself since for my personal things I don't need a full fledged application like Nagios, I just want to get told if something like a hard drive fails. Right now there's plugins for checking systemd services, drives, IP address, sending data to/from other heartbeat instances (super janky), sending notices through pushbullet, dweet.io, blinkstick, and pulling URLs.